I hate my opponents for this

Every time I learn a new opening, my opponents just not play that line. 

When I learn an opening, 90% of my opponents seem to know I like playing that opening and don’t play it. Can someone explain why?

Example, I learnt many common lines of the Italian Opening, then 80% of my opponents play d4 or Ruy Lopez, then I learn those openings and my opponents play some random stuff.

I think this is one of the reasons why new chess players are advised not to study openings. The common argument is that you would be better off spending your time studying tactics and working on you calculation skills, rather than memorizing deep lines in one particular opening.

I think there's a balance though. Decide what opening you like to play as White, and learn like the first five moves or so. Have a plan for what to do against common responses, but don't try to memorize every possible variation. When Black, have a plan for what to play against 1 e4 and 1 d4, but only for a few moves. Don't worry about all other possible odd-ball openings. This is my approach, anyway.

Sub 1000 level players don't play book openings well at all. That is why focusing on openings until you reach about 1200 is not really advisable. If you respond to 1.e4 with e5 then you will need to know what you are going to do against the Italian and the Ruy Lopez. They are the two most common openings and are played at all levels. If you are wanting to force your opponent to go into an opening you know better than them then I would advise playing something like the French Defense or the Caro Khan against e4. These openings do not work against d4 so well because they are defenses against e4. The Kings Indian Defense might be good against d4 for the purposes of limiting what you have to know what to respond to.

As @Jasonosaurus stated it is better to focus on tactics. The other thing is to focus on the opening principles, and if you are going to try to learn lines focus on why you are making the moves, and the ideas behind them. That will guide you better than memorizing a variation that goes right out the window when they make a different move. I advise beginners to focus on three thing in the opening. These are 1. The opening principles 2. Tactics 3. Not Blundering. These will get into a playable position every time. Also getting good at this will help well into the future. There are many times that I have to face an opening that I am unfamiliar with due to my opponent liking to play to these off beat openings. Also trying to learn all the responses to your opening choice is not advisable due to you rarely facing certain variations. Ex. I rarely face the wing gambit in the advanced variation of the French Defense. It is not that good of a response for white in the advanced variation. Due to that I never see it when playing people close to my skill level. If I do face it I am probably playing someone much weaker than me, and I will be able to beat them with out knowing much on the opening theory for that variation.

That's why I don't learn opening theory lol can be helpful but usually your opponents just don't play it

I like Englund gambit

Oh they play it. You just aren't studying properly if you don't know how to respond.

Opening theory is about understanding why each move is played AND WHY OTHER MOVES ARE NOT!

For example, after the moves 1.e4 e6 2.d4 d5 3.e5 c5 4.c3, let's talk about Black's 4th, White's 5th, and Black's 5th moves.

If all you can tell me is that Black should play 4...Nc6, and then White should play 5.Nf3, and then Black should play 5...Qb6 or 5...Bd7, and you are going to cry and bellyache if something else is played, then you don't understand jack bleep about the Advance French! Yes, those are the 2 main lines. Some alternatives are fine, some are bad. If you know Advance French theory, you can answer why.

Black's 4th move - So Black's idea is to go on an all out assault either on d4 or on the queen side. So much so that he is willing to hem in his LSB to get c7-c5 in in one go, what makes the French different from the Caro-Kann, where Black's play is slower and he spends 2 moves on the c-pawn, just to get the Bishop outside the pawn chain. Now we will go into detail of White's 5th move in a moment, but after White's most common reply of 5.Nf3, the idea for Black is to either play 5...Qb6, going all in on d4, and not giving White time to just develop normally and castle as 6.Be2 (this move itself is fine, although 6.a3 is White's best move) cxd4 7.cxd4 Nge7, the move 8.O-O?? is a blunder as after 8...Nf5, White loses material, either the d4-pawn, or 9.Be3 Qxb2. The other idea is rapid queenside development and immediate chipping at the center from the other side. 5...Bd7 (ready to play ...Rc8 a any time) 6.Be2 f6!, immediately coming at White's center. After 7.O-O fxe5 8.Nxe5 Nxd5 9.dxe5, Black has a target on e5 while White will have to decide after 9...Qc7 whether to hold the pawn positionally with 10.f4 or to rip the center with Black's king still there with 10.c4, allowing Black the pawn to open up his own king and to gain tempi on the Black Queen.

But to say "Black should play 4...Nc6" is horsebleep, and crying about it when Black doesn't just proves you know nothing.

Black can also, legitimately, play 4...Qb6. It still attacks d4, and has 2 ideas in mind. One of them I will point out at White's 5th move. The other, although not thought of as being "as good", but White still must know what to do, is to spend extra time to get rid of the Bad Bishop. Black's idea is 5...Bd7 and 6...Bb5, looking to trade.

White's 5th move. Assuming Black played 4...Nc6, is 5.Nf3 White's only choice? The idea is to cover d4 and e5. Why does White want such a firm grasp on those two pawns? Does he need pawns on those two squares? No! He needs domination and control of those two squares, whether occupied by pawns, occupied by pieces, or simply controlled and not occupied. The point is to keep Black's pawns on e6 and d5, and make the Bishop on c8 suffer. That is the whole point of the Advance French. If successful, White gets a space advantage and a raging kingside attack, especially on the light squares. But can White play something other than 5.Nf3?

The first move that comes to mind is 5.f4. It looks like it dominates the e5-square more than 5.Nf3 does. That is true, so a frontal attack with 5...Bd7 and 6...f6 would make little sense now. But d4 is now a bigger problem. Why? Because now, with no pawn on f2, the moment you castle, you have to worry about tactics on d4. Black may be able to take enough times on d4 to make you recapture with your Queen. If that was the end of it, with a White pawn on f2, no big deal. But now ...Bc5 pins the Queen to the King. So everything is tied to overprotecting d4, and attacking moves like Ng5 are not possible due to this issue. So 5.f4 is dubious at best. But Black must know to go after d4 and not e5 in this case, even if you normally play the 5...Bd7 line. This will play more like the 5...Qb6 line.

White could, though, resolve his queenside issues and slow down his own kingside operations, basically slowing down Black rather than attack himself, by playing 5.Bd3 Qb6 6.Qd2, guarding b2, normally the job of the Bishop, slowing down White's queenside development, especially the rook on a1. Remember I said there are 2 reasons to play 4...Qb6? I mentioned one. Here is the other. If you are one that prefers the 5...Qb6 line over the 5...Bd7 line, you might want to play 4...Qb6 and after 5.Nf3, don't play 5...Bd7, but rather, go back to the main line with 5...Nc6, and what you did was avoided this 5.Be3 line as 4...Qb6 5.Be3? allows 5...Qxb2.

So 5.f4 is weak, 5.Be3 is fine, but preventable. What else? What about 5.Ne2? I faced this once OTB and he was lost by move 18. Why? We see the problems with f4. So following with f4 leads to the same d4 issues. This scenario is even worse. Now the knight can't move due to d4 tactics, and the Bishop is now hemmed in, so g3 and Bg2 will take an extra move to get ready to castle. And if f4 is not played, e5 is weak, and Black's attack is on e5.

So in reality, White must know the 5.Nf3 Qb6 line in the event of 4...Qb6. Otherwise, his choices are 5.Nf3 or 5.Be3.

Black's 5th move - Can Black, assuming 4...Nc6 5.Nf3, play something other than 5...Qb6 or 5...Bd7? He can. 5...Nge7 or 5...Nh6, both looking to get the Knight to f5. With 5...Nh6, Black must be willing to deal with the doubled h-pawns in return for the Bishop pair if White takes the knight. With 5...Nge7, White can play 6.Na3, aiming to go to c2, over-protecting d4. Without Nge7, Black could trade on d4 and take the knight and double White's a-pawns and weaken c3. Here he cannot as his own knight blocks.

This is the meaning of knowing theory. Not just memorizing moves and then throwing a temper tantrum with some ludicrous whine post on chess.com like that of post #1.