I suspect that when there are several lines that move relatively fast, people are blind to the lines that have no people in them. For example, at the airport, at the Alaska Airlines checkin counter, there are invariably five or more completely unused self-checkin stations, and a bunch of doofuses (doofusi?) standing in line waiting for the stations that have people. So today I just cut. Similarly, I often notice that the cars leaving Seatac Airport, which has a bunch of lines for people who pre-paid their parking, will tend to queue up on a couple of stations even though others are open and empty.

This doesn't happen at the grocery store. People there are like vultures.