Busting out (again) has shown me where I think my failing is:

Every book I've seen says to be cautious for example with a flush when there's a pair on the board. A guy could have a full house.

And I always seem to think "Yeah, but does he?". The way I play I don't require the nuts in order to bet on the end. Just because J7 can beat me doesn't mean opponent has J7, does it?

Apparently it does. This is especially troublesome at the tiny limits that I'm stuck with now. When people consistently show down unimproved Q2, I get the idea that you don't need the best hand to win. So I'll play fast with cards that are good (like top 2pair, or trips with weak kicker) but not great.

Now and then a guy won't have the nuts, and I'll win like that. But because I'm semi-jamming the pot on all these hands, the win doesn't make up for the losses.