Warning; Heavy spoilers ahead! Do not read if you haven't beaten the game.
We are used to be able to fix things in games. Beat the big bad boss, save the world, achieve success. So while the stated mission in Outer Wilds is "explore", I automatically adjusted it to "stop the sun from exploding" the first time that happened. What do you do then, when you slowly realize during the course of your exploration that the sun does not explode because of some machine you can turn off or some meteor that hits hit. It's simply old. The entire universe is. It's dying its natural death.
I am not fully used to this in games, because games usually have an happy ending. I say usually, because we are gradually seeing more and more games daring to go another route. But when that happens it's usually some tragic ending. Outer Wilds ends with everyone and everything gone. The universe is no more. And yet it is filled with hope and optimism. Because you, as the youngest member of your species rickety space program, manage to get to the thing that started the universe. You, the member of a whimsical, goofy and curious species, did so with the help of an ancient long dead species. A species with technology so far beyond anything you could make yourself. A species that when crashing in a new solar system ends up with lifeboats on two different planets, then manages to rebuild a new system-wide civilization in the span of one generation. They are so smart, clever, scientifically minded and curious. Yet they died out. It was no fault of their own, it was pure bad luck. But they died. Only for you to set out and do what they didn't manage to. And because of that, you, with all of your knowledge get to start a new universe.
Both of these species are so happy, cheerful, so in awe of what the universe has to offer. Every new discovery is met with glee, every new corner eagerly rounded. All of this knowledge is in the mind of your player character, a young and hopeful Hearthian. I can only imagine how wonderful a universe someone like that can set in motion. A universe where someone down the line can sit around a campfire, roasting marshmallows with their friends.