We have nearly 100 billion neurons in our brain—about the number of stars in our galaxy—and they must all act in a particular way in order for us to exist precisely as we do. Similarly improbable, as Richard Dawkins wrote, “The potential people who could have been here in my place but who will in fact never see the light of day outnumber the sand grains of Arabia.” For that sperm to meet that egg, and so forth. We exist and function, literally, by luck.

And yet it feels good not to believe in luck. It’s comforting to think that someone or something is in strict control. In the 16th century, theologian John Calvin believed “all events are governed by the secret counsel of God.” That has long been the basis of most Western religions: You may not know why something is happeni...