Anything you're ever proud of will be thrown away. (2.10)
Our narrator isn't just dissatisfied at the realization that he will die; he's dealing with the fact that everyone else will die, too. And one day, all his possessions and accomplishments will be gone and forgotten. This train of thought can go from dissatisfaction to depression real fast.
Nothing is static. Even the Mona Lisa is falling apart. (6.21)
The Mona Lisa is a great example of something considered a timeless work of art. But it's still man-made, and nothing man-made is going to last forever. Except for Twinkies.
Ever since college, I make friends. They get married. I lose friends. (7.71)
Ah, the circle of social life. Friendships are born, burn bright, and fade away. Any twenty- or thirty-something can relate.