While bumbling around the Eagle, Aldrin stepped on a switch. Which switch? The circuit breaker that would power the ship off the moon in order to rendezvous with Michael Collins in the Columbia. That switch. In fact, we have the transcript documenting how the whole thing went down:
Aldrin: Houston, Tranquility. Do you have a way of showing the configuration of the engine arm circuit breaker? Over. (Pause) The reason I'm asking is because the end of it appears to be broken off. I think we can push it back in again. I'm not sure we could pull it out if we pushed it in, though. Over.
Don't let the tone fool you -- the conversation was the equivalent of the Titanic calmly asking if there was a way to repair an iceberg stab wound. Since the breaker for the engine was the only thing that could fire the engine to get them off the moon, Aldrin inadvertently Apollo Thirteened the whole mission. After telling mission control, they were advised to sleep a few hours while Houston came up with a plan to fire Eagle back up. As if pondering the implications of getting Gilligan's Islanded on the moon was good nap fuel.