Who never doubted, never half believed. Where doubt is, there truth is - it is her shadow.

Certainty that has never been questioned is thinner than it looks. A belief becomes properly yours only after you have genuinely considered that it might be wrong and kept it anyway, which is why doubt tends to accompany conviction rather than oppose it. People most sure of themselves are often the ones who have examined least.

Whatever you hold most firmly, spend twenty minutes with the strongest case against it. If it survives, you own it more fully than before. If it does not, you have learned something worth more than the comfort you gave up.