Repression:

Randolph M. Nesse:

"I suspect that keeping some desires out of consciousness is a major function of repression. We can get only a fraction of what we want. Gaps between what we have and what we want generate envy, anxiety, anger, and dissatisfaction. Keeping unsatisfiable desires out of consciousness not only avoids mental suffering, it also allows us to focus on projects that are possible, instead of ruminating about those that are not."