Life is short, people sometimes say, to convey the idea that you should do what makes you happy. But now that we’re living longer and retiring later, the opposite is also true, though the meaning is essentially the same: Life is long, so look ahead and pace yourself. Rather than being too single-minded about it, there’s probably time to test out new ideas, dreams, and directions. Or, as T.S. Eliot poetically put it, “there may be time for a hundred visions and revisions before the taking of a toast and tea.”