An object or outcome has “motivational magnetism” for an agent when that agent exhibits approach-oriented behaviors toward it. For example, when you hold a piece of bacon and ask your dog if he wants a treat, and he stares intently at you while cycling through his repertoire of tricks, you know that that piece of bacon is a motivational magnet for your dog.
If you’re building a mobile app or game, you want to design an experience in which your user will feel the pull of lots of motivational magnets. For example, if you’re designing Clash of Clans, you want the user to see some fancy troop — a baby dragon, perhaps — and feel motivational magnetism for that dragon.
How do you, the game designer, create this situation?
Start by repeatedly running the user through a loop in which he gets some new troop without much effort and then gets rewarded, perhaps by seeing his new troop lead him to victory in a battle. Eventually, you reveal to the player some troop that exists in the game (ie the baby dragon) and is superior to his best alternative for a goal that he cares about, but that he can’t get until he completes some task. Now he’ll feel that motivational magnetism for the new troop.
So it’s scarcity that breeds pull.