Men operate like a Hammer. Women are like tuning a carburetor.
Women should be thankful men are so easy to please in a relationship. I've never understood why a lot of ladies don't understand that. Honestly, it's like taking care of a baby to some extent. Are we hungry? If no, move on to Has he had a BJ/sex today? If no, remedy. If yes, has had a guys night out in the last couple weeks? If yes, then ask him what's wrong. That's pretty much it. You don't need a 500 page book or a magazine to solve this equation.
There may be a minority of men who fall outside these rules, but they probably need some time with a mental health professional.