Why doesn't Odysseus kill cyclops when he is asleep?

Odysseus refrains from killing the Cyclops while he is asleep because the Cyclops is the only one who can move the large stone blocking the cave's entrance. If Odysseus were to kill the Cyclops while he slept, he and his men would be trapped in the cave with no way to escape. By keeping the Cyclops alive, Odysseus increases their chances of making a successful escape.