I've been at least peripherally aware of Touhou for a long time; the Bad Apple!! video was a big deal in my friend group, even though none of them cared anything about the source of the song or characters. Occasionally I'd try to look it up, but it seemed impenetrable because of how much there was.
Then when Smooth McGroove did his cover of UN Owen Was Her!? I finally saw Touhou gameplay for the first time, and instantly knew I needed to play that game. Now it's several years later and I still can't 1CC any of the games (or even make it through with continues in most cases) but I have a blast playing the games, listening to the music and reading the manga.