"One cognitive symptom of depression might be the loss of optimistic, self-enhancing biases that normally protect healthy people against assaults to their self-esteem. In many instances, depressives may simply be judging themselves and the world much more accurately than non-depressed people, and finding it not a pretty place."
A few other quotations on point:
"The power of accurate observation is frequently called cynicism by those who don't have it." -- George Bernard Shaw
Cynicism is an unpleasant way of saying the truth. -- Lillian Hellman
Egotism is the anesthetic given by a kindly nature to relieve the pain of being a damned fool. -- Bellamy Brooks
Every age is fed on illusions, lest men should renounce life early and the human race come to an end. -- Joseph Conrad
The cynics are right nine times out of ten. -- Henry Louis Mencken
Thanks to Aphorisms Galore!