The strength of the strong nuclear force. The mass ratio of the proton to the electron. The cosmological constant. There are roughly thirty numbers like these — fundamental constants that physics measures but cannot derive. They are simply what they are. Their values are extraordinarily fine-tuned. If the strong force were two per cent stronger, hydrogen would not exist. If the cosmological constant were larger by a factor visible only in the sixtieth decimal place, the universe would have torn itself apart in its first second. Cosmologists call this the fine-tuning problem. It demands an explanation, because the alternative — that we live in one impossibly lucky universe out of trillions of dead ones — feels suspicious in a way that physics does not usually allow. Three explanations dominate. The multiverse: countless universes, we happen to be in the one that works. The anthropic principle: of course we observe a universe that allows observers. And the third, the one that is hardest to dismiss without a reason: the values were picked.