It's the same as saying "If I don't get close to people, I won't get hurt again". It works, if you're not someone who feels sad by not being close to anyone that is.

Fukube's saying that he feels a lot better now that he doesn't give a shit about anything since when he inevitably fails to be any good at it, it won't hurt.

I'm not sure how much time's passed since the whole arc where he tried beating Oreki, but that even could have worked both ways. Fukube sounded pretty laid back since the first episode, so he probably adopted this stance back then already. The festival got him to try for something again, and confirmed his theory that he's doomed to fail at anything he tries.. and thus he's even more set on not trying anymore.

It's not too different from Oreki's run-in with Irisu - except Fukube didn't get the encouragement Oreki did from Chitanda.