Fighting sin is a lot like a karate chop.
I know a guy who decided to quit looking at porn and quit masturbating. He came to me and expressed some concern about the concept of never looking, ever again, and never touching himself, ever again. It's understandably hard to think about it, much the same way it would be for a drug addict to imagine never using their drug of choice, ever.
I told him, "Your focus is wrong. The sin is still the focus of your attention, even if you are saying 'I'm focusing on not sinning', because NOT sinning still puts the focus on the sin."
When we focus on not sinning, we still put the focus on sin--it's just what we do with it is different. The focus should instead be, How could I glorify God now that I'm not sinning like this?
This is why I'm saying that fighting sin is a lot like a karate chop. I've heard (and am not sure if it's true but will use the analogy anyway because that's how I roll) that when you go to break a board with a firm chop or punch, the focus should NOT be the wood. You want your hand, or fist, to get to a point two feet or so past the board. Just take your hand, and move it very quickly from where it's at, to the point behind the board. Guess what: The ultimate goal of breaking the board has been achieved but the focus was different.
The reason why they say to aim past the board is because when your focus is on the board itself, whether you realize it or not, your fist actually slows down enough that you will probably fail. Much the same way, you will probably fail if you focus simply on not sinning. You will sin though, and it's going to sting. It'll sting when you break the board as well, but not as bad as when your fist is stopped cold.