Ever seen this? The toilet paper holder has two rolls. Its easier to keep toilet paper in the stall if one roll is completed all the way, so this sticker is placed on a random roll.
That’s the seemingly logical explanation. But the true explanation is that one roll has mutated, and by chance has generated this sticker. The sticker will extend its life at the expense of its compatriot, giving it more time to reproduce and pass on this beneficial mutation. Natural selection at work.