Design guru Don Norman decided to confront a common toilet paper crisis: the problem of the roll running out just when you need it most. When remodeling his home, Norman installed a dual-roll toilet paper dispenser, under the theory that there’d always be a second roll available for just such emergencies. But he quickly found that, for some reason, both rolls seemed to run out at the same time!

Norman applied some logical thinking to his problem, resulting in the article Toilet Paper Algorithms: I didn’t know you had to be a computer scientist to use toilet paper. The gist of it is that Norman and his wife were subconsciously selecting whatever roll was larger at any given time, leading them both to become roughly the same size, thus running out at the same time. (Read the article for more details on the various available toilet paper algorithms…it’s neat.)

For the record, Norman determined that the optimal strategy for using toilet paper in a dual-roll holder is to always use the smaller roll. This will tend to drive one roll to become empty, but will leave a full roll available.