“Doubt is the act of challenging our beliefs. . . . This is an active, investigative doubt: the kind that inspires us to wander onto shaky limbs or out into left field; the kind that doesn't divide the mind so much as multiply it, like a tree in which there are three blackbirds and the entire Bronx Zoo. This is the doubt we stand to sacrifice if we can't embrace error—the doubt of curiosity, possibility, and wonder.”