Openings and other lessons

I study the openings over and over yet when I actually play the opponent doesnt make the moves he or she was supposed to do! I am asking myself what is the point of studying these lessons?
Maybe someone can help me out ?

Thanks

If you don't know what to do when your opponent leaves the book, then that's a clear sign that you are wasting your time studying openings.

At the 1000-rating level, there are half a dozen other more useful things that you could study.

Tactics. Model mates. Endgames. Pawn structure. Central formations, and their effect on middle-game planning. Old master games from before the computer era.

It's definitely a problem at your level and why in depth study of openings isn't recommended until you are much higher rated.  You mentioned lessons though.  If you are talking about the Lessons on Chess.com, they really don't go much in depth at all.  They're designed more to give concrete examples of opening principles than anything, and as such, they serve their purpose.  Just try to figure out how to punish your opponent if they fail to follow principles, and if you can't do that just develop safely.  

A brief note: If there's a move that is played early on (like really early on 3-5) that for some reason doesn't exist in any database, it's most likely a really bad move lol