Everything you read, say, hear, seen.. is stored in your subconscious mind, since the day you were born. So that's why when you have a stimulus, you tend to remember your past, even if you have not thought about it for a long while. And when you ponder upon an examination question, you may come up with an answer because you are using what you have stored in your subconscious mind.
The sad thing is, no one knows how to fully ultilise it. If we did.. everyone would be geniuses.
Amazing?
p/s : read it in an English comprehension passage