What do you believe is true even though you cannot prove it?
There’s a great little column in the NY Times where they asked a bunch of scientists that very question. The respondants include some pretty famous names, including Richard Dawkins, who has been one of the more influential people in shaping my worldview. Take a look.
Personally, I agree very whole-heartedly with the statements from Dawkins, Nicholas Humphrey, and Alison Gopnik.