What is optimistic nihilism?

I always hate having to write "Kurzgesagt - In a Nutshell," because it's such a wtf mouthful. But they make beautiful animated explainer videos, so I have to write "Kurzgesagt - In a Nutshell" a lot. They are always great, but this 6-minute guide to thinking your way out of existential dread might be their best video yet. The graphics are stupendous.