You are waiting in line, and must decide whether or not to stick it out or bolt. How do you choose?
Most people look back and see how many people are behind them in line. If the line behind them is long, they tend to stay in line and wait. And if they do quit, they are most likely to quit in the first three minutes.
Making this kind of comparison could be economically rational. A long line means that if and when you have to come back, you will be forced to wait anyway. So why not just get the waiting over with? (Note that the researchers try to control for this effect, although imperfectly.) A long line also suggests that many other people value the good or service, which again implies that waiting is worthwhile.
But that is not the primary hypothesis of the researchers, nor is it how I think. When I look back and see many people behind me, I feel that my lot in this matter is not so bad, and that I should stick it out. So I do.
The short article on this research is from the December issue of Psychology Today, but the article itself is not yet on-line. Here is the home page of one of the researchers, including a full citation to the article in Journal of Consumer Research. Here is a on-line summary of the work.