Trees Are Weird

The purpose of a tree, as far as the tree is concerned, is to gather sunlight and water. The fact that a tree magically converts those things into building material and fuel is the purpose of a tree as far as humans are concerned. But first, trees had to compete with all other plants to get that sunlight, so they grew tall. The trees had to come up with a system to gather and utilize water over distance.

That system relies on physics that are hard for humans to replicate. It also depends on a form of cellular suicide. The upshot is that even when a tree is healthy and functioning, a majority of it is dead. Kurzgesagt explains what's happening on the inside of a tree in a video is less than ten minutes long; the rest is promotional. (via Nag on the Lake)