You don't need an opening reportoire until you hit 2000 ELO - ture or false ?

Exactly. They will discredit a perfectly valid point or rebuttal, simply because they didn't like it, whether it has merit or not. The font might be too big or small, your punctuation of spelling might not be perfect, etc among even more trivial reasons.

Really? Because I don't know how to argue without ideas :)

Paradox's examples I guess would work. A grammatical correction is unlikely to allow us to discover a new idea. And you will see, strangely enough, I never make such a correction! Because frankly I just don't care -- if I saw the person's idea I don't have a whole lot to gain by it being spelled right anymore.

I think that while it's true, you cannot make it above 1800 without having a solid idea about the ideas that are occurring within an opening. So studying of openings are essential but by going through master games very quickly to get a sense of what your plan is after your 12th move or so. Memorization serves a limited purpose and unless excess time is available, other things would serve the U1800 player better. By 1800-2000 more understanding is definitely needed.

But in all honesty these types of questions are very generic. If you find that by move 14 you don't know what to do, make poor moves and are lost within certain openings, then not studying master games within those openings would be remarkably foolish - a foolishness I adhered to for quite some time just to obey "don't study openings". Then I realized I keep losing immediately after the opening is over so no point in continuing to memorize different types of rook endgames because if a certain opening comes up I will never make it!

Again there is ambiguity. I mean, teaching opening principles to someone who doesn't know them will result in massive improvement. Teaching theory that depends on memorizing 13 moves in multiple variations, not so much. It's much easier to overestimate the importance of theory than it is to underestimate it.

I think, psychologically, a lot of people would like to think that if they get a nice position, nothing could go wrong. But then in a game when they reach that position, and they suddenly have to figure out what to do next, things get tricky again. And if they lose concentration for one moment they may blunder and lose their hard earned advantage. People underestimate the practical difficulties of taking the plans you have about a position and actually carrying them through. Just because you can say what you would do in a certain position doesn't mean it would be easy to actually carry it out if you were to actually have to play that position in a real game.

I would agree that you don't need a FULL opening repertoire, but it would be handy if you knew your stuff for the black pieces and could atleast get developed without losing as white. You definitely need to understand pawns.

Just play random moves and if you're good, you'll win.

For the middlegame planning and pawn structures.  Maybe some defense too, which is kind of covered in endgames where the inferior side has to demonstrate great technique for the draw. 

Elubas, there's a difference between argumentation and obfuscation. 

FiveofSword's point in 324 and 325 is very well stated. I have the same experience with my students, and I also teach tactics from the opening.

Rdc is also correct that memory is important in chess. It isn't that hard to develop memory skills. Think of the lines in chess as being similar to lines of poetry, or lines in a play.

Just about anyone can memorize lines. The problem for most players is that they think that memorizing lines is the same as learning the opening. They're wrong. 

"Elubas, there's a difference between argumentation and obfuscation."

Well sure they're not identical terms. I want to argue as well as possible for the sake of everyone; if I fail I fail. I'm not going to be able to say things in a way that everyone will like.

I remember a junior advancing from 1800's to 2000s within a year who played as White mainly 1.e4 e5 2. Nf3 Nc6 3.Bc4 Bc5 4.c3 Nf6 5.d3! and 1.e4 e5 2. Nf3 Nc6 3.Bc4 Nf6 4.d3! followed by c3. It's a good, sound opening, probably second-best White option after Ruy Lopez (at least Larry Kaufman states something along these lines), and with minimal theory load. The only problem is that it teaches about positional buildup, not about tactics. But if we add 1...e5 as Black and let the opponent bring tactics to us, then this deficiency is counterbalanced.

This reminds me of the idea of someone learning how to procreate versus someone learning how to be a parent....

My GM Coach also told me that.No need to study opening until 2000.

But now i am trying  french for black and d4 for white :)

Your coach is giving you bad advice.

I think that is a cliche. If you work on openings, and you learn them well, you study the middlegames belonging to those openings. I have a chess student rated around 1500, and I still teach him to play the Slav. I want him to learn the logical structure of the opening, the idea of solving the bad bishop problem, of grabbing a pawn if white doesn't make a concession, of the pawn breaks c5 and e5. Chess starts at move 1, and every player should have a basic idea what to do on that move and the next ones.

(It should not be left unmentioned that I also torture the guy with rook endgames until stuff like the Philidor position haunts his nightmares.)

You need to know some things obviously but you don't need to be reading Avrukh and others. We just had a funny game in the US Championship that included h6 and g5 lol. I'm not saying this is a good idea but as long as you aren't blundering you should at least have something to hold in the middlegame.

You are hardcore. He pays for this?

There is nothing magical about the number 2000 (that I am aware of -- are you Harry Potter?).

It's just dumb.

I know how to learn. Study all aspects of the game. Oldtimers tell you this 2000 thing. It is ridiculous.

That doesn't mean he is not a great coach. It's just what he was taught.

Everything according to their level. In the beginning you learn the basic ideas (like development). Then you learn a few moves in the major openings. Then you slowly add associated middlegame ideas and sidelines.

To work for a full repertoire before 2000 is probably a waste of energy. Just like taking a break from tournament play to master Dvoretskys Endgame Manual at 1500 would be a waste.

It's hardcore to teach them chess?