Ever since reading Don Norman’s classic “the design of everyday things” forcing functions became one of my favorite topics. I always keep a sharp lookout for them.

In the example above you can see the thermostat of a typical German shower. By default the maximum adjustable temperature is 38° Celsius (100 F). That’s hot enough to soften the hardest dried-up dirt but it still feels comfortable to shower. If you want to go for the extra boost of heat, say after a winters night out in the cold, you have to push the red button to be able to rotate the thermostat beyond the 38°C limitation.

I guess the forcing function was implemented to save you from accidently burning your skin. It can happen easily. You know what I mean. Take for example those awkward moments at the beginning of your bathing experience, when you wait for the water to get hot and then all of a sudden it does get hot – hard-boiled eggs hot. Traveling a lot lately gave me insights into the scientific world of adjusting water temperature: an interesting topic indeed, given the multitude of influencing factors like handle design, thermostat placement, clockwise/anti-clockwise rotation, different water pressure of hot/cold water pipes, delay of temperature change etc.

But in the above example: once again saved by the simple pleasure of thoughtful design.

What is your favorite forcing function?