Will considered what to do. When you choose one way out of many, all the ways you don't take are snuffed out like candles, as if they'd never existed. At the moment all Will's choices existed at once. But to keep them all in existence meant doing nothing. He had to choose, after all.
The Amber Spyglass by Philip Pullman (who is a genius at mocking the "only the easy stuff for the kids" convention)