The New Zealand Story when I was 6-7 years old comes to mind. The first boss of the game is a flying whale that I just couldn't beat. So I did what you did back then: ask a friend at school the next day. "Oh, you're not supposed to beat him normally. You gotta jump into the whales mouth before you can kill it"
You have no idea how much time I wasted, trying to get into that stupid whales mouth. And remember, we're talking 8-bit style check pointing (i.e. not good) and finite lives here. I eventually beat him after abandoning my friends advice, and chalked it up to him fucking with me.
Don't ask me why, but I got to reading up on the game some weeks ago. There was apparently a bazillion versions of that game, with small differences across platforms. Like how you killed that whale: in the SMS version you just shoot it to death. In the Amiga version you have to jump in it's mouth. I think you can figure out where I'm going here, right?