The way to being successful is really about knowing yourself and being committed to something. Sure, there's going to be some rough patches along the way unless you are extremely special. I wouldn't really count on it, so I say just continuously outweigh the benefits and costs to something and look for something that really fits your boat.
It's really important to my thinking that one doesn't go after something really illegal like becoming a hit man or being paid to steal stuff for someone! I read about this one kid who turned killing into a career and when he was caught, he had no remorse for it and somehow ended up being sentenced to life in prison. Being old and forced not to do something you don't like is not a very fun way to go in life.
Therefore, pick something that's legal or at least even if it's a little shady like you are feeling bad about taking people's money, make sure you can get away with it and it doesn't really hurt anyone while being agreed upon. No lying or cheating, but using skill. Obviously, bluffing can sometimes be a skill, but don't do it to gamble upon someone's physical life!