Sometimes, we spend so much time getting to know a game that our drive to replay the programmed missions dulls; and in exploring the world, we create original objectives to work toward. Or sometimes, a game is simply too easy as-is, so we must add new restrictions to challenge ourselves as we play.
In these situations, we make self-imposed challenges: games within games, whose rules we ourselves build and must honor, as the most purely self-imposed challenges are not defined at all by the game.
These can range from completing the famous Nuzlocke challenge, to playing single levels using only a certain powerup, to avoiding using your character's primary action (and even minimizing presses of the button that activates it), to playing hide-and-seek with an item in the game. Surely you've attempted something along these lines?
What self-imposed challenges have you tried over the years, and have you ever created any that you'd like to share?