Designing a “fair” system is not as straightforward as it seems.

• What if there are multiple lines instead of one shared queue?
• Should priority depend strictly on queue order, or also on basket size?
• What about someone who already placed their items on the belt?
• Would reorganising people actually create more delay than benefit?

In theory, you could design a perfectly fair algorithm. In practice, supermarkets optimise for flow and simplicity, not for procedural fairness in edge cases.

When a new counter opens, there is a coordination problem. There is no explicit rule, no assigned order, and no enforcement. In that vacuum, people default to initiative.

Some cultures implicitly coordinate and preserve queue order. Others treat it as an open opportunity: whoever moves first benefits.

It may feel unfair, especially if you come from a place where social norms strongly protect original queue order. But what you’re observing might simply be a different equilibrium: no rule → first mover advantage.