Rachel Kroll has learnt to avoid "the stupid hour":
The next day, not only will you have a nice place to resume, but you'll also have the benefit of several hours (or days, if over a weekend) of subconscious/background processing you didn't even realize was going on. It'll make for a better result overall.
Next time you get stuck on a problem or thought, try taking a walk. Some of my best problem solving moments have happened during a lap around the block.