(Excerpt from Zero to One by Peter Thiel)
To a definite optimist, the future will be better than the present if he plans and works to make it better.
A definite pessimist believes the future can be known, but since it will be bleak, he must prepare for it.
To an indefinite optimist, the future will be better, but he doesn’t know how exactly, so he won’t make any specific plans.
An indefinite pessimist looks out onto a bleak future, but he has no idea what to do about it.