Pessimism is all about mindset and we can actually train our brains to be more optimistic.
Practicing mindfulness is a great way to reduce pessimism.
Mindfulness is about living in the present moment and allowing things to pass us by instead of dwelling on them. Allow yourself to feel negatively about the event for just a moment and then let it pass by.
Practicing gratitude frequently also helps decrease pessimism. Gratitude is the act of showing appreciation and contentment for our lives. The more we focus on the good, the more good we get!