There's a shop that serves pudding. They serve two flavors: butterscotch and chocolate. They don't ask what flavor anybody wants, because they think they already know. Everyone's preferred flavor is assigned at birth, and it's even written on everyone's driver's license and/or other forms of ID. Usually, this works out. Almost everybody is content to enjoy their assigned pudding flavor for their whole lives.
A few people don't like the flavor they have been assigned. Technically they are free to switch to the other flavor, but it can be difficult because the shop is stubborn. They just serve you the pudding flavor they think you always wanted