I like thinking about things like this, but it's not depressing to me. I find it liberating: no matter what I do it will only matter to those who matter to me.

Let's say that humanity (or its progeny species) could exist for ever. YOU will still be forgotten when everyone you've ever known dies. Even if you had some great achievement in life, you will be forgotten eventually. 1,000,000 years from now it seems doubtful that whatever species is the descendant of humans would care or remember who Archimedes is.

So either way, it's inevitable that you will have no grand impact on the universe or even our species. Embrace it. It's freedom. Stay home when your daughter is sick, she'll remember it, but your boss won't remember you coming in. Etc.