constructive pessimism 

Believing one's own work is not good enough or that something in their work is missing, causing them to revise or even restart their work.

A writer had completed five pages of a script before feeling that their story just wasn't good enough, and so constructive pessimism struck them as they searched for that missing oomph.

constructive pessimism by joob1 January 11, 2022

Das's Law of Optimism/Pessimism 

The glass is twice as big as it needs to be. Get there.

Das's Law of Optimism/Pessimism is derived from something said by George Carlin. It explains that sometimes you expect too much of yourself and it gets you down in life.

Das's Law of Optimism/Pessimism by Mindbladeskillyaks June 16, 2010