Agent-centered constraints on harming hold that some harmful upshots of our conduct cannot be justified by its generating equal or somewhat greater benefits. In this paper I argue that all plausible theories of agent-centered constraints on harming are undermined by the likelihood that our actions will have butterfly effects, or cause cascades of changes that make the world dramatically different than it would have been. Theories that impose constraints against only intended harming or proximally caused harm have unacceptable implications for choices between more and less harmful ways of securing greater goods. This leaves as plausible only theories that impose constraints against causing some unintended distal harms. But, I argue, given the distal harms our actions are likely to cause through their butterfly effects, these theories entail that any way of sustaining our lives is overwhelmingly likely to involve unjustified killing, and that we are therefore morally required either to allow ourselves to waste away or kill ourselves.