Self-checkout bias

The supermarket in my office building has two queues. One feeds a bank of six human checkout operators and the other feeds a bank of eight self-checkout machines.

In my experience so far, the human operator queue moves significantly faster than the self-checkout queue. Furthermore the self-checkout queue is noticeably longer than the human operator queue. This is despite there being two more self-checkout machines than human operators.

It seems to me that people systematically over-estimate their own ability to efficiently self-checkout. Leave it to the pros, I say!