My two:
Very cliché, I played Ocarina of Time a ton as a child, have memories of playing it both on N64 as a wee child and on game cube as a less small child. Never got past water temple even with the game guide.
Yu-Gi-Oh forbidden memories. Played the crap out of that game on play station, constantly playing on free play praying for the cards I would need to get further. I was never able to beat more than 1-2 of the high mages. Watching speed runs on the game it turns out I was never ever going to beat that game as a kid. The final 6 are just disgustingly brutal.
Daggerfall. I played that game to death and didn’t even make it past the third or fourth quest.
Eventually I’d give up and just wander off to do whatever I felt like. I must have visited every major city and country, but never set foot in one of those annoying dungeons :)