Moloch is the personification of the forces that coerce competing individuals to take actions which, although locally optimal, ultimately lead to situations where everyone is worse off. Moreover, no individual is able to unilaterally break out of the dynamic. The situation is a bad Nash equilibrium. A trap.
It happens when "In some competition optimizing for X, the opportunity arises to throw some other value under the bus for improved X. Those who take it prosper. Those who don’t take it die out. Eventually, everyone’s relative status is about the same as before, but everyone’s absolute status is worse than before. The process continues until all other values that can be traded off have been – in other words, until human ingenuity cannot possibly figure out a way to make things any worse." - Scott Alexander
One example of a Molochian dynamic is a Red Queen race between scientists who must continually spend more time writing grant applications just to keep up with their peers doing the same. Through unavoidable competition, they have all lost time while not ending up with any more grant money. And any scientist who unilaterally tried to not engage in the competition would soon be replaced by one who still does. If they all promised to cap their grant writing time, everyone would face an incentive to defect....