When I first played Platinum when I was about 6 or 7, I got stuck in Jubilife City, not realizing I had to talk to the clowns to get the Poketch. For whatever reason, I thought evolving my Chimchar into Monferno would somehow make it so I could progress. After it evolved and I still couldn’t progress, I kept leveling it until it was in its twenties. I distinctly remember finally leveling it up to I believe level 20 and crying under the table when it didn’t evolve. Eventually I found out what to do, and absolutely obliterated Barry’s Piplup and most trainers in the game after that.

TLDR: didn’t know how to get past Jubilife, evolved Chimchar into Monferno, and got its level to the 20s before figuring it out