Some guy posted a question on how many opening lines one should know and how deeply they should be memorized. The best answer was, if you’re not a master, none. Study strategic/tactical themes that are the result of common middlegame positions from your opening of choice. That way when an opponent plays something you haven’t seen, at least you will know whether or not his move fits in with the requirements of the position. If it doesn’t you know he made a less than optimal move and by being familiar with basic middlegame themes and patterns that result from your opening, you will be able to plan correctly.
He thought that was crappy advice. His idea is to memorize 30 lines 8-10 moves deep. Reminds me of the guy who once wrote a letter to the editor claiming that if one could memorize Modern Chess Openings, he could become a GM and challenge the Russians.
Anyhow…the guy went on about how he rarely loses, so either he’s really good in which case he does not need to be asking such a question in a forum haunted by amateurs or he’s playing really weak opponents. The other possibility is he knows nothing about chess and isn’t interested in learning.
Case in point: Once upon a time my 1400-rated opponent took about 5 minutes for his first 20-some moves while I used about an hour and a half. Finally he sank into deep thought and after several minutes played and outright blunder and resigned a couple of moves later. In the post mortem I had to listen to him yammer on and on about what a bad move I had played. When I asked why it was so bad, his only answer was that it wasn’t the move Fischer played in a game he had memorized. It didn’t matter because once “out of the book” he didn’t understand the position.