How does one learn opening theory?

The question might sound pretty stupid, but... it's very difficult to learn a ton of variations from a ton of openings and systems and it also seems futile. Is it right to focus on one or two openings and learn them as good as possible and prepare one or two replies for the others? What is the right approach?

No answers?

      You learn opening theory the same way you learn ending theory, except in reverse!

Well... it is futile for amateurs because our opponents don't play big theoretical lines anyway.  If both players are below master it's rare to get deep into a theoretical line.

Yes, it's good to focus on an opening until you've learned it well and gotten some experience.  Variations are useful after you understand the ideas.  First thing to do with an opening you want to learn is understand the nature of the middlegame you're headed towards.  What each side wants to accomplish and how.

To do that get a coach, book, or play over a lots of example games.  (A good book will have lots of example games, a good coach will have you look at games too).

For the positions in between your preparation use basic principals, calculation, and good judgement.

Thanks for your answers. I didn't say that I do not know theory at all but my knowledge is fairly limited.

LOL he never implied that he didn't know any theory nor is it hard to believe that even if he didn't, he could make 1600+. I am sure it has been done many thousands of times.

I am, for the first time in 40 years of chess, making a real effort to learn my openings for OTB play.

I am using Chess Position Trainer. I have already typed in lines I am planning to learn, Now I just picked a number out of hat as far as minimum depth goes for all the lines I have, and I just slowly increase the number. I am aiming for breadth not depth. I accompany this with books for understanding. Its a long term project. Openings have always been by far my weakest area when I compete OTB.