Toilet Roll Effect

To put this in a more formal-sounding way, it can be observed when there are two independent cues that stop or start your behavior, and the behavior is something whose change tends to be one-way.

In order to wipe certain parts after you have finished doing certain things, you wind some length of paper around your hands, cut the paper from the roll, and use it.

Let's say you are used to use 1-ply toilet rolls, but you noticed that 2-ply rolls were on sale at the market, so that is what you bought recently.

What happens?

Because you are so used to the hand-motion to wind the 1-ply toilet rolls (say, you always wind 4 times), you still wind the same length of the stuff. Your backside starts to be comfy with the extra fluffiness your hands are giving it by using more paper. After all, you are winding the thicker 2-ply paper the same number of times. You may start winding the stuff a bit fewer number of times, but the rate of such decrease is slower. Perhaps you learn to wind only 3 times, but it would take time for you to go down to 2, which is the half of the original.

Next week, you notice that 1-ply rolls are on sale, so you switch again. By this time, your hands are used to winding 3 times, but your backside now complains because it no longer is rewarded by the same fluffiness. After all, you are giving it less paper. So you end up start winding the stuff even more, until your backside gets comfy enough. Your hands may learn to wind 5 times by the time this happens.

Notice that there are two cues that makes you stop winding when you do this. How many times you wind the paper around your hand, and how much fluffiness your backside feels by being wiped by it. And the change in the amount of paper you would use tends to be one-way (using more is easier).

Imagine if you switch to 2-ply rolls again. And then switch back to 1-ply rolls. The consumption of your toilet rolls tends to increase, and increase more if you switch between 1-ply and 2-ply rolls more often.

Exactly the same thing happens to cigarette usage, by the way. Two competing cues are how often you take a break, and how much chemical effect you get from a puff. Start from a weak brand, and your break schedule may settle for a break per 3 hours. Switch to a stronger brand, and your body gets used to greater chemical effect with the same 1 break per 3 hours schedule. Switch back to the weaker brand, and now your body will complain and wants more nicotine, and your break schedule ends up being more frequent. Switch back to the stronger one again, with the more frequent schedule, your body gets trained to more nicotine. Rinse and repeat...