The mistakes made by doctors are innumerable. They err habitually on the side of optimism as to treatment, of pessimism as to the outcome.

Optimism is denial for chumps with no life experience".
"What's pessimism?" I said.
"Religion without God.

So desperate was Kugel for things to turn out for the best, proclaimed Professor Jove, that he couldn't stop worrying about the worst. Hope, said Professor Jove, was Solomon Kugel's greatest failing.

I will be the first to admit that I am a pessimist by nature. It is, after all, the wisest way to be. We pessimists have everything to gain, whereas optimists have a fifty-fifty chance of being disappointed.

The man who is a pessimist before 48 knows too much; if he is an optimist after it he knows too little.

No misfortune is so bad that whining about it won’t make it worse. (Apr 2007 Gen Conf)