So you have a game with lots of hidden areas, secret stashes of powerups, and generally all kinds of rewards for exploring and busting down walls. You're at the end of the game and have every powerup you've seen, but.. why is there still an empty slot in your inventory? Why hasn't that bridge been fixed? What did you miss? Where is this undiscovered item? How do you get to that area?! See also Interface Spoiler for another videogame meta-trope based on expectations.