Winning a game at 1400 rating is literally impossible.

Hello, 2030 uscf here. I can tell you with confidence your problem does not stem from not being able to memorize opening theory. What your problem comes from is not understanding the positions from the openings. For example in this kind of position:

You almost never push the pawn. White's setup is fine - forcing the matter won't help. What will help is getting the rest of your pieces into the game. What happens is that you overextend - your pawns are too far forward and you cannot protect them properly. This is a thematic idea in almost every opening that has people push their pawns.

Some of your problems can be solved by thinking through it a bit more:

Here you played ...Ke7.

which is strange, since if you don't take it, then white just moves his bishop, and your king is on e7 for no reason. But if you take the bishop, you at least get a bishop, if temporarily. Even if white can get the piece back (he can't), at least your king isn't blocking your bishop and queen. If you took the bishop, you may have been able to see that Qf3+ is met with simply ...Nf6, and if dxe5 then Qe7 pins the king.

But most of the time mistakes around 1400 level stems from a lack of applying chess principles (not really opening principles). stuff like "if you are more developed, open the position even at the cost of some pawns", "attacks on the wing should be met with central counters", etc.

Additionally, your tactical vision seems to be lacking. You can spot one-movers but you can't spot opponent's two-movers. I would encourage you to work on tactical themes like deflection and overloaded piece if you can, otherwise it would be difficult to even get back up to 1400 rating again.

lol

Studying openings does not necessarily mean memorizing openings.

I looked at a few different games than you posted. I looked at 3 of your last games vs 1400+ opponents. I think I see some patterns that will help to point you in the right direction. 

In general, when players (like me) say that you should only focus on opening principles instead of opening theory, I mean that you must adhere to the following opening principles:

1. Control the center. For white that means: try and get e4 and d4 as a pawn center, black needs to prevent white from getting that center (or immediately break it up if white does manage to achieve it). 

2. Develop all of your pieces as fast as you can. That also means as efficiently as you can. Don't put your pieces in the way of themselves and get them to their best square in one go. 

3. Get your king safe.

Game 1:

While I'm not a fan of 5. ... Qf6, because you don't want to develop your queen too soon and you deprive your Ng8 from its natural developing square, I want to point out 6. ... Ba5, 7. ... Bb6, 8. ... Nd4, 11. ... Ba5. In 11 moves, you've played the same piece over and over again. The most important general principle of opening play is to get all of your pieces out as fast as possible. Each piece needs to hit their perfect square immediately if you can. That means that you're not allowed to play the same piece twice in the opening if you don't have to. Notice the difference between an opening and a middlegame. In a middlegame, the manoeuvre Ba5-Bb6 might very well be a good idea to get your bishop to a better position. In the opening though, you're not improving your position enough by getting the bishop to b6, because just developing a piece from the back rank or castling will improve your position more. I also want to point out that move 11. ... Ba5 just gives away a piece in 1 move: they just have to take it. 

Game 2:

I like the beginning part, where you try and get the e4-d4 center with white. Black does well to immediately break it up with ...d5, but that's a fine way to try and control the center. After that, you needed to start developing. Here you do a much better job of developing all of your pieces as fast as you can. My only problem is with that knight on a3. You want to develop your pieces towards the center. Na3 is a terrible piece. Here black also makes a mistake though: 10. ... Nb4. You take full advantage of this with 12. Bd2, developing with tempo. Without you knowing theory, you have a great opening advantage after move 13. If not for that knight on a3, it might even have been close to winning already. The fact that you've lost this game in particular has nothing to do with your opening play. You just give everything away by first blundering the d4-pawn with 18. Qh3, and then with 20. f5, 21. h4, 22. Rxf5 you manage to give away material with 3 moves in a row. You've lost the game on tactics, just like game 1. 

Game 3:

Again, looking at it from a opening principle perspective, I think 4. Bd3 is a bad move. This isn't efficient development. You can see you need to move the bishop again to free your other bishop and your queen. That makes you lose time and therefore it's a bad developing move. 4. Bc4 is better, as it also looks after the center more. I wonder if you noticed that e5 was also hanging, otherwise that's your first tactical mistake. The second one comes down to why you played 4. Bd3: you wanted to protect e4. But if you see a bad move that solves your problem, you always should try and work out whether a better move doesn't also solve the problem. Here 4. Bd3 is bad, like I already said, but solves the problem of e4 hanging. 4. Bc4 is better and if you'd work it out, it ends up also being good enough. Because after 4. Bc4, Bxc3; 5. dxc3, Nxe4, you can play 6. Qd5 with attacks on e4, e5 and f7. They'll have to play Nd6, you can take the pawn back on e5 and be much better developed than your opponent, while they also have a goofy knight on d6 that'll make it hard for them to develop their queenside. Your opponent really helps you out of a jam by taking your knight on c3 though, so you don't suffer much. 

8. Be2 is also again moving the same piece twice. Just play 8. Qd2 or 8. g4 and then develop your queen so you can castle queenside. Compared to 4. Bd3, this is just a small thing. 

Again, the opening looks pretty decent. You even win a pawn. Why did you lose? Because you missed a 1 move tactic with 12. ... Nxe4. And you lose some more by another tactical error with 18. g4. 

To summarize:

Yes, your openings can still get a little better. That has nothing to do with theory though, it has to do with applying your opening principles better. You take too many liberties when it comes to moving the same piece twice. The real problem though? Tactics. You lose because you give pieces away. Often without your opponent having to do anything special. The problem could be twofold. First it could be that you're not focusing enough on your opponent's ideas. If you don't stop to think what they could want to do with their position, you'll also not notice where they're applying pressure on your position. The second one could be that you stop your tactical calculations too soon. Try thinking half a move deeper than you used to. So instead of thinking 'I do this, you do that then I can do this' you try and think deeper: "I do this, you do that, then I can do this, but you can do that". Especially when lines are seemingly forcing, like in the last game where you play g4, you should try and work it out until the forcing moves stop and then at least be able to know the resulting material score. 

I think you shouldn't be discouraged: your play in general is quite OK. I definitely don't think you should be studying opening theory. In fact, compared to some openings by your opponents, I think some of your own openings are better than theirs. I gave you some pointers that I would focus myself on, but nothing more than that. The real difference between 1200 and 1600 opponents is tactics though. The stronger you get, the less often people give away material with 1 move blunders. The stronger you get, the more people will calculate tactics correctly. That's the part of your game that still needs a fix. 1600+ players won't crumble to scary looking tactics, they'll take the money if they calculate that there's nothing to be scared about. 

If you do want to start studying something, I would suggest middelgame strategy. I agree with #22 that you've come to a rating group where a deeper understanding of the game will soon be needed. I disagree though that this is the thing holding you back at the moment and there are some things you shouldn't yet try and study as a 1400 (like initiative and the other dynamic imbalances). Deeper understanding of what to do with an open file, could've helped you in game 2 for example, where I think doubling on the c-file looks promising. Don't put any time in studying opening theory though. It's a time and effort drain, and the goal of opening theory is to get or prevent small advantages for white. At your level, tactical mistakes swing the advantage much more than that.

Look at this latest game. This idiot beat me with the stupidest opening of all time.

https://www.chess.com/game/live/53012966435

He beat you because he played a slightly bad move and you went overboard, sacrificed a piece, and didn't play energetically enough after the sacrifice, so he won with his extra piece(s). The opening he played isn't as bad as it looks.

But... black's opening was better than yours... you're white in that game right? You were down a piece on move 4. 

Not even close to the "stupidest opening of all time", and you completely misplayed it.  You can make that sacrifice work, but not with passive play (though, even with energetic play, it is only roughly equal and you are still trying to attack before your pieces are developed).

Oh, Bxf7 is a known move? Ok but...

Look... you can accomplish a heck of a lot by just having good fundamentals. GMs say that you don't have to start consciously making a study of breaking principles until something like 2200 FIDE (which is what, 2500 chess.com or something).

 - Place (and usually maintain) a pawn in one of the 4 central squares
 - Bring your knights and bishops out quickly, ideally to influence central squares (when in doubt retreat your bishop to f4 or e3, not h4)
 - Castle to a side where few (ideally none) of the 3 flank pawns have moved
 - Play a pawn break against one of your opponent's center pawns (e.g. white plays d4 against a pawn on e5)
 - Use the newly opened lines to infiltrate into the opponent's side and / or come into contact with long term weaknesses (long term weaknesses are backward, isolated, doubled pawns and the king).

Do all this while not giving away pieces for free, and also take pieces for free when they're offered.

Yes this is hard and takes years of practice... but sometimes... I'm a bit annoyed when people post games where they open with 10 pawn moves then ask what went wrong. If you can't finish your development quickly without losing material then we can't even have a conversation. There's nothing to say. Learn the basics and do them.

It's a 20 move game and your bishop is still on c1. If it's on c1 because you were busy winning material or conducting a mating attack, fine, but otherwise I don't want to see that kind of crap

You gave away your bishop on move 4. I mean, what do you expect? 

I could have written your opening post word for word, only where you have written 1400, I would have to substitute 1200. 

I've played over 400 games here....you've played a lot less. Respectfully, I'm not sure, given all this data, why you're a 1300+. I hope I can say that without sounding like an insult, but a person's true rating is at a level where they would win half their games, no?  So if you're not winning half your games......well, I'll stop there, because I have no doubt that you're a better player than I and don't want to offend. 
I got to 1127 and then started losing. All the way down below 1000. When I got to 1000 I started winning again. Because I got back in my groove? I don't know....maybe because I was playing players on average 100 points lower. 

I missed a win with Nh4 today after a bishop sacrifice. I know the feeling of being an idiot all to well. Just keep playing, work on your tactics and analyze your losses or draws.

https://www.chess.com/game/live/53025679787

Yep, keep playing because the next game can be a score of 96% accuracy. I can say this because I am a 1400 so I feel ya:

https://www.chess.com/game/live/53028573825

For much the same reasons: neglecting development, hanging pieces, missing 1- and 2-move tactics.

Here, despite the multiple mistakes and blunders, I still missed Nd4 for the win lol. Enjoy 1400, we get to make mistakes and look like idiots:

https://www.chess.com/game/live/52453249681

The first game you lost because you didn't take the bishop on f7 and then you decided to move the knight away instead of taking the bishop which allowed the skewer to win the queen. If you look at checks (and when your king is exposed like that looking for checks is a must. You should always look for checks, don't get me wrong, but not looking for checks when your king is exposed is especially bad, it is like overtaking on a solid line vs overtaking on a double white line).

The second game you had to see that when you played 10.Na3 to defend the fork on c2, your opponent could remove the defender by playing Bxa3. When you defend something important like a c2 square, you need to be paranoid about your opponent removing the defender. Your opponent doesn't even see that and he plays 11..Nxe2+ instead. With the removing the defender tactic in mind, you had to play 10.Be4.

Third game:

Again, when you have a pawn or a piece which is only defended by another piece, you need to be careful about removing the defender tactic. You can't allow your opponents to play 10..Bxg3 removing the defender of the e4 pawn. Technically speaking, allowing 10..Bxg3 wasn't a blunder but only if after 11..Bxe4 you spot a tactic. In every position you should look for undefended pieces. Bishop on e4 is undefended, so is the pawn on g7, which is why you have 12.Qd4 fork.

Fourth game:

Undeveloping the knight on move 7 was very weird. I would have just played h6, preventing the bishop to pin my knight. Seeing opportunities for your opponents to pin you, deciding when the pin is dangerous enough to be stopped is a skill that you gain with experience. Since your opponent already has a knight on d5 and you are unable to put a bishop on e7 the pin on the f6 knight is dangerous and it should not be allowed.

Yes, 1400 blitz is stronger than 1400 rapid. Rapid ratings are inflated compared to blitz ratings. 1400 blitz maps to 1550 rapid. 

https://www.chessratingcomparison.com/Graphs

Don't play fast chess play long games so you can think what is going on.  Don't play like the internet says (most of your opponants have seen the videos, lastly don't play what your opponant wants make him/her nervous.)

Have fun.

I see you are a gold member, therefore do your allowable 25 rated puzzles every day. It’s how I was able to defeat 1700+ players:

https://www.chess.com/game/live/51214226355

https://www.chess.com/game/live/24620535969

https://www.chess.com/game/live/19074986763

You gave up a bishop on move 4 for suspicious compensation, but ok, it is not the end of the world even though you shouldn't play such moves. Just moving the bishop back to e2 would be perfectly fine and then claming that your bishop on e2 is better than his knight on a5.

After you sacrificed the bishop you needed to develop quickly, not allow him to consolidate. Something like 6.Qh5 threatening Ng6+ winning the rook on h8 because of the pin and X raying the knight on a5 looks reasonable to me and if black responds with 6..Nf6 then you play 7.Qf7+ Kd6 and his king is marching up the board. 

However, I don't like that after 6.Qh5 black can play Qe8 and I don't see a good continuation. So maybe, play castles or d4 on move 6. The problem with Qh5 is that your opponent can win tempos chasing around your queen, especially since you can't allow a queen trade.

6.d4 to open up the bishop, control the center, defend the knight seems reasonable. Castling on move 6 also looks reasonable.

You played 6.Qf3 and Qf3 is met with a natural and healthy developing move Nf6. You have to expect that 6.Qf3 will be met with 6..Nf6 and therefore play something else, like d4, castle etc.

On move 7 you played d3, that's too passive considering that you have sacrificed a bishop, go d4 instead. d3 also takes away a retreat square from the knight. Your opponent will obviously try to get rid of the annoying knight on e5 if given the opportunity, it is nice to have the d3 square for the knight then.

After that you proceeded to hang a knight on move 8.