I'm a chaperone on a school trip of some sort and we are walking students up a spiral staircase that seems to go on forever. After a while of climbing, it becomes apparent that some students have parents who want them to come down already, while other students really really want to go to the top. The problem is that the staircase is so narrow that there is really only space for one person at a time. It is up to me to come up with the sorting algorithm to ensure that the students who need to get down to the bottom get down as soon as possible while the students who want to go up get to the top as soon as possible. I start off suggesting that all of the kids take one step backwards, and angry students clambor all over me in a panic to get to the top instead.