The Princess is in another castle. The Princess is in another castle. GAH. Seems that stupid Toad says that every time you finish a level in Mario. But science shows he, in fact, doesn't.
No, it has now been proven - and this is proven by science, so it's without refute! - that she is only in another castle in 87.5% of occurrences. Or, in catchier terms, seven out of every eight times.
So one in eight, you're good to go. And now you know. And knowing is half the battle!