It happened to you at least once in your lifetime. A fragment of a song insisted on following you around. You tried to hum and whistle, but it wouldn’t go away. A friend told you that you need to listen to the whole thing; your brain kept the song on repeat because it didn’t remember how it ends. So you played it, but it did not help.
A song is not the only kind of thought that can follow us around.
We insist on reliving our most humiliating failures.
We take each conflict we were a part of and turn it around in our heads for as long as it takes to find an angle that makes us look good.
We keep hearing the most hurtful words our loved ones have spoken a long time ago.
Funnily enough, we don’t pay half as much attention to our triumphs, successes, or the good we did. Who knows, maybe that’s why stories about good people don’t sell very well.
If you want your characters to seem like real people, they should be the same. Being stuck on a thought is a great motivator or a turning point for any character arc.