Catechism of the Catholic Church

Another temptation, to which presumption opens the gate, is acedia. The spiritual writers understand by this a form of depression due to lax ascetical practice, decreasing vigilance, carelessness of heart. "The spirit indeed is willing, but the flesh is weak." The greater the height, the harder the fall. Painful as discouragement is, it is the reverse of presumption. The humble are not surprised by their distress; it leads them to trust more, to hold fast in constancy. (2094, 2559)