All the time!
I dont consider myself a master painter by any means, but would say I'm above the novice level.
I find so many things can put me off my game so to speak, usually something else in life seemingly unrelated
tbh.
If you're painting and realise that youre not in the zone.. perhaps its time for a break or to stop the session entirely

quite often I will sit down to paint and just find myself looking at it for a while and then decide not to
lol!
- its not like the average monkey work job that can be done alseep. Its a creative art form. Your personal physical or emotional state, can and will drastically affect the work quality (in both good and bad ways). Do you imagine that Picasso couldve just sat down at any time and banged out a master piece?
Far from it! It takes lots of planning, thinking and experimenting before you start to get to that point in a project
tbh.... allthough I dare say its not totally unknown for people to just be a godamned creative genius everytime they every try