If I find myself stuck for more than a reasonable time on a single bug, never plough on.

Get up, listen to some music, relax on your memory foam mattress, close your eyes and simply relax. Get back to your workstation and I always find myself solving it within seconds and wondering, "SHIT, WHY DIDN'T I THINK OF THAT BEFORE"

And I find myself answering it's because I never took a break!