What's something you realized when you reached your late 20s or early 30s?

I realized that if the average age to die is around 77, I've lived nearly half of my life. And the older I wait to have a child, the more unfair it would be for the child.

Having to bury your parent at only 20 something or 30 something years old is probably rough. A lot of people don't bury their parents until much later in life.
What's something you realized when you reached your late 20s or early 30s?
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