Ask HN: What are the big/important problems to work on?

I keep seeing critiques against working on tasks that are meant to maximize user engagement. A recent comment that I saw on the subject went in the lines of: <these are not the big/important problems of our lives>. Therefore my question comes because I cannot seem to see by myself what the real problems are.

A short argumentation would be valuable too, just so it's understandable where you come from.

Thanks & Happy Monday!