I recently did the Coursera mooc on gamification with Kevin Werbach (by did, I mean watched the videos). I'm now going over my notes.
On of the things that was emphasised was that in thinking like a game designer, we make the participants, whom we treat like plays, as the centre. We want to give them opportunity to learn, advance, progress, climb up the leaderboard, etc. It has to be challenging but fun. And then I remembered this scene from Wreck It Ralph. Don't interfere with the player, guide them