For me, it would be that I smoke weed
That I never did Something Great™ with my life.
Didn’t become a rock star, didn’t cure cancer, didn’t invent a world changing technology, didn’t become a famous artist, etc.
I didn’t know specifically what I was aiming to do, but for some reason I assumed that i would do something that made a big impact on the world. I was totally convinced of it. And it’s not because my parents constantly told me that or anything. The closest i heard was a lot of “you have so much potential if you’d only apply yourself!” Ugh.
Do you have kids or a partner?
Because that made a significant impact on their world.
Maybe at your age. At my age almost all of the Something Great bells have rung. Don’t get me wrong, there are still plenty of very meaningful things i can accomplish, and many important impacts i can make on individual people’s lives, - but for me the possibility of doing something that has a broader impact on society is pretty much gone. But so what, the impact i can have on individual people’s lives is still very valuable, and my own subjective experience of life is just as important as anyone else’s! So i try to make my own experience of living as good as it can be!