Depression is not generalized pessimism, but pessimism specific to the effects of one's own skilled action.
Robert M. SapolskyDigestion is quickly shut down during stressโฆThe parasympathetic nervous system, perfect for all that calm, vegetative physiology, normally mediates the actions of digestion. Along comes stress: turn off parasympathetic, turn on the sympathetic, and forget about digestion.
Robert M. SapolskyThe gigantic challenge is the magnitude of the individual differences in the optimal set point for "good stress." For one person, it's doing something risky with your bishop in a chess game; for someone else, it's becoming a mercenary in Yemen.
Robert M. Sapolsky