In Brief: Why You Always Seem to Choose the Slowest Line at the Supermarket

By Norman Chan

Queueing theorists have an answer.

Adam shared this awesome story yesterday: an explanation for why it's so difficult to choose the shortest line at the supermarket. The answer lies in queueing theory, or the mathematical study of how people wait in lines to best optimize and predict wait times. According to queueing theorists, simple probability explains why your chances of choosing the fastest line in an scenario with lots of line options is small. In a perfect world, a single long line at the supermarket that funnels into the next available checkout counter would be the most optimal (like a bank or post office line), but human psychology rejects that. We would prefer to take the gamble of trying to find the fastest of multiple lines at the store--it gives us the illusion of control and the hope that we can beat the system.