Did you ever daydream that you're a wizard? Or maybe an astronaut, or a superhero, or a secret agent? Perhaps when you snapped back to reality, you were left with an internal grin and a feeling of "heh, that would have been cool. Oh, well." Let's assume in your fantasy you were an astronaut, because although they exist, you probably aren't one.
Possibly you've had that dream, or one along the same lines, several times. Maybe more, now you come to think of it, and they started... hmm, as long as you can remember? Nothing strange about that, all kids daydream about that kind of thing. Astronauts are rare, but they've been around since before you were born, and occasionally show up in films and on TV. But when they do, they're the object of ridicule: the other characters treat the astronaut as some kind of freak, and joke about them. I don't get it, you think: being an astronaut sounds pretty cool. But your friends and family don't bat an eye at these films. You take note: astronauts aren't cool, and you'd better not let on about that daydream.
Life goes on, you grow up, and most of the time when you drift away from whatever conversation you're not listening to, you're thinking about being up there in orbit, or walking on the moon. In your spacesuit. Yeah, that would be nice. Once or twice you may read about or see a documentary on actual astronauts, and while you pretend not to be interested, every word etches itself into your memory. Just some more trivia to add to your general knowledge, you tell yourself.
You'd never deliberately seek it out, but coming across information about astronauts is always a happy acccident, and you're glad to fill in any gaps in your knowledge. You know the training schedule pretty much by heart. In all the interviews, the message is the same: "I always knew I wanted to be an astronaut; I told my parents about it almost as soon as I could speak." Strangely, you feel almost jealous.
Perhaps you have some posters of the moon up in your room. Or maybe a discreet NASA logo on your shirt. Or played an astronaut in an RPG. It doesn't mean anything; you're just so secure in your identity as "not an astronaut" that you can do it without feeling ashamed. In fact, it's almost... exciting?
One day you come across a post by someone about your age, who gave up their career as an accountant to join the space program. Turns out they didn't know all along, and just figured it out one day. That sticks in your throat a bit: some folk have all the luck. Wait, what?
You can't shake the feeling that there's something missing from your life. Something big. It's not like you're depressed, or anything, but everything just seems so... gray. Pointless. You don't hate yourself, but you wouldn't be too bothered if it all just ended one day.
And then, at last, you figure it out.