Sleeping makes you smarter
As detailed in the article: Sleep on It: How Snoozing Makes You Smarter . When you sleep, your brain is still active - it processes the information that was absorbed during the day, in a more efficient way than during the day, thus improving memory recall. So when you have difficulty solving a problem, it really is worth 'sleeping on it', even if just for a couple of hours. Maybe I should get more sleep...