[marginalia_nu]

I think the most common failure mode is neuroticism; getting stressed and frustrated with the lack of progress, thinking about the progress toward the outcome rather than the problem to be solved. Stress in particular is extremely poisonous to thinking. The expectation should be that it takes as long as it takes, and you need to be calm and well rested.

[wizzwizz4]

If you find yourself choosing between working on the problem and taking a nap, always take the nap. (Given the choice between remaining in bed, and taking another peek at the problem, usually take a peek at the problem, after which you should do what feels best.)

Some experimentation should convince you that this is how human minds work (well, most of 'em, and yours is probably one of them), after which you can employ this strategy without guilt during a crisis.