There isn't much point learning ending theory until your games tend to get that far. Some chess teachers don't properly understand their job.
That must be the reason why the russian chess school has been so unsuccessful.
I do not know whether the Russian chess school produced less happiness than others. But they certainly produced the best results for decades. And one of the best known facts about their methods is: Endgame first.
Endgames are more interesting than openings... and it would be a great consolation if I was great at endgames even though I lost hundreds and thousands of games in a row in the opening (without a single win or even draw). 
Absolutely not true.
I am rated 1250, and after I started taking openings seriously, it is not rare for me to be A WHOLE MINOR PIECE UP in the opening. Imagine that, because I know my openings, I can just start the game with knight odds or bishop odds. How can you say that isn't an advantage?
However, I enjoy learning openings very much. I think it would be different if you enjoy different things.
And I agree with what some people said about how learning the middlegame plan after the openings is as or more important as memorizing the opening moves.
Here's a decent example:
Even with my crappy 1200 rated skill, knowing the opening can give me big advntages straight from the get-go.
sorry, but the "theory" did not help you, it was opening principles that helped you. the only reason you won material was tactics and your opponent not following opening principles. good attack though.
Absolutely not true.
I am rated 1250, and after I started taking openings seriously, it is not rare for me to be A WHOLE MINOR PIECE UP in the opening. Imagine that, because I know my openings, I can just start the game with knight odds or bishop odds. How can you say that isn't an advantage?
However, I enjoy learning openings very much. I think it would be different if you enjoy different things.
And I agree with what some people said about how learning the middlegame plan after the openings is as or more important as memorizing the opening moves.
Here's a decent example:
Even with my crappy 1200 rated skill, knowing the opening can give me big advntages straight from the get-go.
Please tell me which theory it was ???
Absolutely not true.
I am rated 1250, and after I started taking openings seriously, it is not rare for me to be A WHOLE MINOR PIECE UP in the opening. Imagine that, because I know my openings, I can just start the game with knight odds or bishop odds. How can you say that isn't an advantage?
However, I enjoy learning openings very much. I think it would be different if you enjoy different things.
And I agree with what some people said about how learning the middlegame plan after the openings is as or more important as memorizing the opening moves.
Here's a decent example:
Even with my crappy 1200 rated skill, knowing the opening can give me big advntages straight from the get-go.
umm.. this isnt a very strong argument towards anything... your opponent broke every opening principle possible, and got beat for it.
If you play something sharp, like the english attack against najdorf or sicilian dragon, grunfeld, you should probably know some theory
as well the common themes that occur in those openings.
otherwise, especially at the 1800+ USCF level, you might be lost of out hte opening.
Absolutely not true.
I am rated 1250, and after I started taking openings seriously, it is not rare for me to be A WHOLE MINOR PIECE UP in the opening. Imagine that, because I know my openings, I can just start the game with knight odds or bishop odds. How can you say that isn't an advantage?
However, I enjoy learning openings very much. I think it would be different if you enjoy different things.
And I agree with what some people said about how learning the middlegame plan after the openings is as or more important as memorizing the opening moves.
Here's a decent example:
Even with my crappy 1200 rated skill, knowing the opening can give me big advntages straight from the get-go.
Why don't they have a facepalm emoticon yet? Something needs to be done!
You guys are right! I thought that in this case, "opening repertoire" was "memorizing opening lines plus opening theory and opening principle". The conversaiton on memorizing opening lines alone is a much tougher one which I do not have the credentials to have (obviously). Perhaps you can see how confused I was now because I thought people were trying to argue that learning opening principles is a waste of time.
I believe I have completed misinterpreted the quote and the OP, but in the new way I see it, this is definitely an interesting idea.
Studying theory is a waste of time if you're just going to make positional and tactical mistakes in the middlegame and endgame.
Yes, but everyone makes these positional and tactical miscalculations in the middlegame, even GMs.
"There's no such thing as a perfect game." https://hbr.org/2015/04/lifes-work-an-interview-with-garry-kasparov
There's a big difference between the types of basic motifs that players under 2000 miss versus those missed by GMs, IMs, etc., which are more like combinations, except in cases of chess blindness.