I know it is a bit of a silly answer but here we go:

My brother had installed a game-boy emulator on the family PC when my parents had prohibited gameboys from the house. My older siblings bought some though and hid them, but i was too young for that. (They also didn't tell me).

Anyways, so at the time Pokémon Ruby and Sapphire was the hot shit. I played Ruby on the emulator and i loved it. There was just one problem. The "nebula" animation that is transparent in the gameboy version was solid in the emulator. When i entered a cave i had to find a way to pass it blindly. This was before we had proper internet access at home, so i couldn't look up the cave layout.

I had to gave up after the second gym or so. When i got older and my grandma bought me a gameboy, i played Ruby like crazy as i finally could progress.