When I first hung out my shingle as a freelance writer, I tacked a postcard over my desk. It showed a picture of the earth from space against a black background. The words were a quotation from the pioneering naturalist John Muir: "When we try to pick out something by itself, we find it hitched to everything else in the universe." It looked a little cheesy, yet felt pretentious, too, which was a neat trick. Inspirational messages generally make me gag, and I wasn't looking to bolster my sense of cosmic significance. But I liked the substance. The quote reminded …