I’ve always loved this poem by Shel Silverstein:
Listen to Mustn’ts, child, listen to the Don’ts.
Listen to the Shouldn’ts, the Impossibles, the Won’ts.
Listen to the Never Haves, then listen close to me.
Anything can happen, child, Anything can be.
It’s a nice promise against the pessimistic voices in the world. Especially when they’re cloaked in self-doubt and coming from inside your own head.