Looking for a book on how to accept an average life

I’ve come to the realization that I’m a mediocre average person and will lead an unremarkable life of unmet potential. I’m looking for a book that can help me come to terms with this. Googling has mostly turned up advice that tries to be inspiring and gives tips on how to start excelling and becoming better than average. But that’s not what I’m looking for (I’m too old for that lol). Any recommendations welcome, thank you!