I am almost embarrassed to admit how much I 'live' human factors. Everything I see around me, I interpret in terms of how well it meets user needs as defined in context. So for example, when I am at the gym, they have an indoor track that has a simple rule. Users run clockwise Mon, Wed, and Fri and they run counterclockwise Tue, Thurs, and Sat. This is because running on a short loop puts a lot of pressure on the outside leg. So running different ways is better for you.
So why is the scheme MWF one way and TTS the other way? It seems that they are spreading the days around the week. If you go to the gym every day, this would be ideal. But if you look at real people, what gym schedules do you think are most common? Experts tell us that we shouldn't work out every day - it takes about 48 hours for our muscles to recover from a workout. So we should do each exercise every other day instead of consecutive days. Of course, this means that users who run on the track are probably running either MWF or TTS. So the way they designed this rule causes each person to run around the track the same way every time, exactly what the schedule is trying to prevent.
This error is caused by the gym management not thinking about how real users use their product. If you ask anyone naive to HF, they will probably go with the MWF and TTS schedules too. But when you point out the irony I describe above, they immediately realize the error. So how come the gym management never does?