The big reveal at the midpoint of the film ‘Moon’ is that Sam is some sort of clone, one in a series of clones that are activated, do their jobs and wear down before being ‘disposed of’, at which point the next clone is activated to take over, and on it goes. The intrigue occurs when a clone is activated when one clone is activated while the previous one is still active, and this revealing the whole set-up to both of them.