

Fiber is, for the most part, indigestible, your body can’t really break it down into simpler sugars that it can make use of.
And just for clarity, just because humans can’t break those down doesn’t mean the entire animal kingdom can’t. So its fiber to us, but usable carbs for lots of other creatures.
I’d change that as : “Being an adult is mostly realizing you didn’t look as bad as you thought you did because the only person that was concerned about that was you. Everyone else was doing their own thing focusing on themselves, just like they are now.”