ive discussed this thought with my husband quite often. we both believe that humans cant handle living forever. i mean, yeah, it would be cool for a while, but i think it would get too overwhelming. people just dont have the mentality to live forever.

I'm going to live forever... I'm going to Learn how to fly... High...

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This was actually discussed on Cracked of all places. Among the things mentioned were the eventual memory overload, evolution eventually passing an immortal by and the also mentioned greedy people experimenting to find your secret.

But to actually answer your question: I probably would eventually grow frustrated with humanity's continual failure to learn from history. I'd like to think that for a few centuries at least, that there would be too many things in the world to keep me from being bored or jaded.