u/Firm_Following3310

I recently had a lecture on Philosophical Pessimism, and though the majority of the class had concluded that they were not, or perhaps more accurately, could not be, pessimists, there was also a struggle to find well-backed-up reasons against being a pessimist. The lecturer was, naturally, a staunch pessimist in every sense of the word and was quite convincing in his reasons as to why human existence is inherently bad, but didn't provide much pushback. What I'm asking is, what are some of the best reasons against being a pessimist, or do most of these stem from merely not wanting to conclude that our existence is bad? Thanks :)