Confusion about learning openings

I will take this down in chunks....
1..learn opening principles-you think it is easier to memorize lines.
1. Opening principles are easy to remember. Castle, knights before bishops, don't move the same piece twice, castle early, respond to a flank attack with a counter in the center(that is a large majority of the principles).....
Now lets try and memorize a line. e4 c6 wait I mean e5, d6, g6, nf6, nc6 or b6(all respectable moves). So after 1 move we have about the same amount of "ideas" as the opening principles. Now lets find a book on c6.....Hey a beggining book on the caro kann(e4 c6) that is ONLY 200 pages. http://www.amazon.com/Starting-Out-Caro-Kann-Everyman-Chess/dp/1857443039/ref=sr_1_4?ie=UTF8&qid=1345642389&sr=8-4&keywords=caro+kann
I think you get the point.
The other point is knowing an opening is not memorizing lines. THere are things like move order tricks to get you into positions which you haven't memorized and just playing moves out of book which will confuse you only if you don't understand the IDEAS behind them.

I am back!!! There IS a point.
Just returned from a tourney where I got my arse handed to me, though I had some winning positions against higher-rated players.
I don't believe tactics alone can take someone to 2000, unless they are supremely geniusly geometrically talented and superhumanly cognitive, like my idol, Michael de la Maza.
I believe opening study is a must (memorization and attempted understanding), even in the U1400 section (at least through moves 6-8), unless you enjoy being rated 1200 forever (I hope to be at that elite level one day).

I bet you haven't been rated in the triple digits in a while.
But I did lose an overwhelmingly won endgame, so your point is well-taken.

I can't say it's not fun to have an edge as white, or to avoid difficulties as black -- it sure is -- but its effects tend to diminish as the moves pass by. As a class A player, I have experienced too many instances of a much better position turning into a draw (sometimes even a loss, although my very cautious disposition favors having few losses, even if this means chickening out a lot), when with good technique I would have gotten the point, or cases where I have a satisfactory position but just get outplayed in an endgame or in positions where piece coordination is highlighted (this is strongly connected to the endgame).
When you have a good endgame (and tactics, but an appreciation of the endgame will often allow you to pay more attention to the geometry of the board, helping your performance with and increasing your appreciation of tactics immensly), it generally is simply very hard to beat you. Even when you are under pressure, you can often escape into inferior endgame positions, or shed off a point in material resulting in the former, force your opponent to outplay you, and claim the half point once he fails. The point is your opponent can never look forward to an obvious blunder from you, and has to be constantly make sure he's not doing so himself.
The above might not sound like it, but this tends to be the worst case scenario for most games a strong endgame player plays against an amateur. And that's a really good worst case scenario. As for this player winning games, all he needs is a small advantage and he can put all sorts of pressure on his opponent, and when he gets a winning endgame advantage he actually wins it, with a lot of consistency. Having that kind of technique tells your opponent that the slightest material disadvantage they get will be their end. Most people have confidence that being a pawn down, even for nothing often isn't so bad because it's such a pain to win; but against someone with technique, it might feel like being down a piece. They might actually quiver in fear at the loss of the pawn, something that would normally be a mere irritation.

No real opening study for me (save for “easy”, entertaining, informative reading, such as from Sadler, McDonald, or Marin), until I am rated 3500 in tactics wherever or 2500 in endgames (Tempo Theory mode). I do, however, open threads about them, even to this day (the more things change ...)
Eagerly awaiting the return of the OTB ... COVID is the enemy bishop, my chloroqueen on the same diagonal, my hopes the rook in between.

Understand the ideas don’t memorize moves
you cant understand the moves without memorizing them. it is impossible
That is an incorrect statement! You sure can understand without memorizing!
Example: You are playing Black, and the moves played thus far are 1.e4 e6 2.d4 d5 3.e5 c5 4.c3 Nc6 5.Nf3 Qb6 6.Bd3. Man, I have not memorized the moves against this line! What do I do? Hmmmm.
I understand that the bad thing about this move is it blocks the Queen from covering the d-pawn and that now, I attack it 3 times with my pawn, knight, and queen. He guards it with his pawn and Knight. So let's see, a little calculation tells me that 6...cxd4 7.cxd4 Nxd4 8.Nxd4 Qxd4 9.Bb5+ is going to lose me my Queen. I have to do something that will make that not be check. Guarding the check with ...a6 is insufficient as it is a big piece I am losing, worth far more than that Bishop. So I must play ...Bd7 to invoke the threat, but if I play 6...Bd7, he can stop it all by taking my pawn on c5, so I better trade the pawns first and THEN move the Bishop, and so I now play 6...cxd4 and if 7.cxd4, then 7...Bd7 and if 7.Nxd4, his center falls apart.
Now I know this subconsciously because I have known this trick for 25 years. However, 25 years ago, I reasoned this out rather than just memorized it so that if it comes with some other garden variety, like 6.a3 a5?! 7.Bd3, I know the differences!

For instance, in one of Marin’s chapters, he gave an introductory couple pages to an opening line he was covering (very well written), but when the actual moves started, in about half a page we were already at move 8 ... with 24 pages to go. Now, how do you reason out moves 4-7 in a non-forcing opening when there may be numerous alternatives? I am guessing using general strategic principles, then attempting to verify that there is not a more concrete refutation (starting with most forcing moves that are common at my level)? It seems like at some point you just have to make an early move choice based on the comments of others (this move leads to sharp lines, this one to quieter lines).
You've received lots of good advice but I completely understand when you say it is hard to follow. E.g. principles are hard to learn, learning the "why" of an opening is not at all obvious, and so on.
FWIW, here are my thoughts: Don't try to memorize openings by move order, but do try to memorize the positions reached in an opening. E.g. I play the Sicilian Dragon. I know that my pawn goes to c5, a knight to f6, pawn to g6, bishop to g7, and I castle king-side. My other knight will usually go to c6, and my other bishop will often move to g4 to pin white's knight. The order of moves often doesn't matter; you can reach the same position by transposing moves. It's extremely hard to memorize all possible move orders that reach the same position, but it's not hard to memorize the position that defines an opening.
Know elementary tactics before you try to learn openings. Pins are a part of many openings, also possible pawn forks or knight forks. And discovered attacks are important. You can't understand openings unless you understand elementary tactics.
Learn the major themes of positions and openings: open or closed, classical or hypermodern. You might prefer the classical style of fighting for the center with pawns in the center, but you will no doubt run into opponents who play the hypermodern style of trying to control the center from outside rather than occupying the center.
That's probably enough for now.