10. As Long As You're Alive, You Can Be Better - As Long As You Put In The Work
This lesson from both shows align surprisingly well, though Steven Universe will, for the most part, be much more optimistic about it than Bojack, with a song stuck in there for good measure.
In Bojack Horseman, this concept is presented both during Bojack's period of sobriety and self-improvement, as well as in the finale, when he fears an eventual relapse. Todd gives him sage advice, telling him that even if he falls off the wagon, he'll get sober again; he has as much chance of getting better as he does getting worse.
In Steven Universe The Movie, the lesson is both sung in Steven's song "Change" as well as reiterated near the end: "There's no such thing as happily ever after. I'll always have more work to do." Though surprisingly sober, the underlying idea is still remarkably optimistic.
Both present the same lesson: You need to put in work to get to a good place, and good things don't just fall into your lap because you feel like you deserve a happy ending. And as long as you're alive, you always have a chance at happiness. As Steven put it:
"Happily ever after never ends."