"... An effective technique is to explain your code to someone else. This will often cause you
to explain the bug to yourself. Sometimes it takes no more than a few sentences,
followed by an embarrased 'never mind; I see what's wrong. Sorry to bother you'.
This works remarkably well; you can even use nonprogrammers as listeners.

One university computer center kept a teddy bear near the help desk. Students with mysterious bugs
were requested to explain them to the teddy bear before they could speak to a human councellor."
-- Kernighan and Pike, 1999