Optimism results in better health, happiness, and success than pessimism. This is true even if pessimists more accurately assess reality. Why does this happen? Well, optimists will keep going while pessimists will get discouraged and give up.
Pessimists may acquire “learned helplessness”. That’s a fancy term for despair. For example, animals who can’t control when they get a reward or punishment usually give up responding to any stimulus after a period of time. This helplessness continues to disable them even in new circumstances.
Optimists consistently see good things as permanent and that they themselves caused that good. Consequently, optimists see bad circumstances as temporary and caused by external forces.
I liked this book, but thought it was definitely quite repetitive. Outside of the details of Seligman’s experiments and tons of anecdotes, I don’t know if I gained much more than I detailed in the TL;DR above.