A pessimist is one who makes difficulties of his opportunities and an optimist is one who makes opportunities of his difficulties.
— Harry S. Truman
Most Powerful Positive Pessimism quotations
Between the optimist and the pessimist, the difference is droll.
The optimist sees the doughnut; the pessimist the hole!

The average pencil is seven inches long, with just a half-inch eraser - in case you thought optimism was dead.

In optimism there is magic. In pessimism there is nothing.
We live in the best of all possible worlds
No pessimist ever discovered the secrets of the stars.

The gravitation constant is the same always.
But the economic constants-these elasticities of demand and supply-depending, as they do, upon human consciousness, are liable to vary. The constitution of the atom, as it were, and not merely its position, changes under the influence of environment.
Confidence isn't optimism or pessimism, and it's not a character attribute.
It's the expectation of a positive outcome.
Every state of welfare, every feeling of satisfaction, is negative in its character; that is to say, it consists in freedom from pain, which is the positive element of existence.

After 5,000 years of recorded human history, you wonder, what part of 2,000,000 sunrises doesn't a pessimist understand?
I don't believe in pessimism.
Are you responsibly optimistic? Pessimism and leadership do not mix.
Leaders are positively visionary.

Creeds matter very little... The optimist proclaims that we live in the best of all possible worlds; and the pessimist fears this is true. So I elect for neither label.
Pessimism is easy. We all can do it. We don't need to read books on how to be pessimists. We don't need guidance on how to think negatively. But we do need guidance on how to think positively. People that write books on how to do that are multimillionaires.
Seeing the glass as half empty is more positive than seeing it as half full.
Through such a lens the only choice is to pour more. That is righteous pessimism