…most of us can tolerate disappointment in one sphere of our existence without getting deeply depressed, providing the other spheres remain undamaged. Normal people may mourn, or experience disappointment, but because they have an inner source of self-esteem, they do not become or remain severely depressed for long in the face of misadventure, and are fairly easily consoled by what remains to them.
Depressives, in contrast to these normal folk, are much more vulnerable. If one thing in the external world goes wrong, they are apt to be thrown into despair.…Disappointment, rejection, bereavement may all, in a depressive, pull a trigger which fires a reaction of total hopelessness: for such people do not possess an inner source of self-esteem to which they can turn in trouble, or which can easily be renewed by the ministrations of others. If, at a deep internal level, a person feels himself to be predominantly bad or unlovable, an actual rejection in the external world will bring this belief to the surface; and no amount of reassurance from wellwishers will, for a time, persuade him of his real worth.