People are smart - they'll pick a self-checkout line or a cashier depending on which will reduce the effort they have to expend. So, even with varying shopper p

People are smart - they'll pick a self-checkout line or a cashier depending on which will reduce the effort they have to expend. So, even with varying shopper preferences for which is intrinsically better/worse, it'll average out to roughly the same effort required across all queues.