The Amazing Fifteen Minute Break

How many times have you been working away on a problem and not been able to solve it, then when you are commuting home or you stop for a snack, you find the answer jumps out at you? For me it is almost a given. Anytime I am having a hard time solving a problem, as soon I step away I the answer almost always arrives. So why is that so many times we find ourselves thinking that we can try that one last solution?