In storytelling, three is a magical number. How many time have you heard that somebody must collect three things, or complete three tasks, or is asked a question three times, or choose between three objects, or make three wishes? The list of examples are numerous. For some reason or other three is a number that lends itself well to storytelling. There is a kind of balance to the number three in which two seems too few and four too many.
Things in threes are most readily noticeable in fairy tale stories, and it is still a beautiful device for telling such tales. But the power of the number isn’t limited to fairy tales and using it needn’t be a cliche, or even very obvious. I’ve found it popping up in my own work quite naturally. In “A Thing Worth Dying For,” the protagonist endures three days of events that test his resolve to do the right thing. Also, “Chiburi” features three flashbacks that serve as a kind of psychoanalysis of the protagonist, taking him further back in his life to the source of his suffering.
Look closely. You’ll see that a lot of things come in threes, and it can be a useful way of seeing things when working out the structure of a story.