I’m not a programmer by trade so I exclusively work on smallish projects, not profit driven but rather interest driven.
Percent of seriously considered side projects that I actually start: ~10-20%.
Percent of projects started that are ‘finished’ to a functional bare minimum: ~50%. Let’s say this is around 20 projects over the past 10 years. Range of maybe 30-300 hours invested per project.
Percent of finished projects that have enough reach or impact to feel successful: ~15%. Of these, probably 200-300 hours invested per project.
If I were trying to do profit-driven projects based on an uninspiring idea to address an uncertain market gap (that I otherwise wouldn’t care about) then I think the failures would be more painful.