"That light," said the Chaplain, "is it going up or coming down?" "It's coming down," said Lord Asriel, "but it isn't light. It's Dust." Something in… - Philip Pullman

It's about wrong and less wrong. Bad and less bad.

Even if it means oblivion, friends, I'll welcome it, because it won't be nothing. We'll be alive again in a thousand blades of grass, and a million leaves; we'll be falling in the raindrops and blowing in the fresh breeze; we'll be glittering in the dew under the stars and the moon out there in the physical world, which is our true home and always was.

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 that moment all Will's choices existed at once. But to keep them all in existence meant doing nothing. He had to choose, after all.