I think about positive things

You know every word of a song you never chose to learn. It was on in a shop, in a car, at somebody's kitchen table, and repetition did the rest without asking permission.

Attention behaves the same way. What gets rehearsed becomes what is easy to reach, which is why a well-worn worry can be summoned instantly while a good memory takes a moment to locate.

That is not a fixed setting. It is a play count. Nothing dramatic changes on the first few repetitions of something better, and then one day a decent thought is simply the one that arrives first.