Posting in the first Pokémon game thread made me think back when my Yellow version was brand-spanking-new and I was a newbie to the franchise. I was so stupid back then!
In the first place, I couldn't figure out how to get out of the house. It wasn't like they made it obvious or anything, but my eight-year-old self felt like an idiot when I finally figured it out (after ten minutes).
A second, much lengthier stupid thing I did was get stuck in Viridian Forest for weeks. Pikachu made it to level 81 in there because I was in there for so long (I didn't bother training anyone else, I guess). I had absolutely no idea how to get out at all. I thought the exit was just a dead end and when I finally pressed against it, I was shocked. Happy, but shocked.
Anyway, share your own dumb experiences so we can all have a laugh. I can't be the only one this happened to!