Optimists generally believe that good things will happen, while pessimists tend to expect the worst.
Optimists go into new situations with high expectations, while pessimists keep low expectations to prepare for negative outcomes.
Nothing illustrates the difference between optimists and pessimists quite so accurately as this illustration from Owl Turd Comix.
In a nutshell, a pessimistic outlook may become a self-fulfilling prophecy, as illustrated above, pessimists are well-equipped to handle life’s downturns. After all, they do spend their lives preparing for the worst.
Not that you have to worry about the optimist in the comic. True optimists don’t mind failure. When life knocks them down, they get right back up and try again.