The design concept I am looking at is affordances.
The Hand Sanitizer Machine very clearly demonstrates what you are supposed to do and how you are supposed to get the hand sanitizer. The image below where it says “Hand Sanitizer” shows that if you place your hand in that opening, then you will receive the cleansing liquid. The product is very simple, and without reading any instructions, anyone can kill the bacteria lurking on their hands.
My roommate bought a kettle in the beginning of the year that has a little movable piece at the top that turns on and off the heat. There is a “1” and “0” labeled with the “0” showing that the device is off and a “1” showing that the device is on. Also, if the device is on, the little see-through piece on top turns orange, so no one burns himself or herself, while the liquid is heating. Also, in order to open the kettle, you have to pull on the little handle above the shadowed part in the overview picture. First of all, that piece looks like it can break, and when I first tried pulling on it, I thought I was doing it completely wrong and was fearful I was going to destroy the lousy contraption. Secondly, when I first tried to use the device, I had a lot of difficulty figuring out how to both, add water and turn on the device because nothing was labeled or based on known conventions. Clearly this is a product that violates the affordances concept, since it is not clear how you add water and turn it on.
As shown in my overview drawing of the kettle, I would make it so that the user can turn on and off the kettle with a button. Everyone knows what the power button looks like and most devices use buttons to change various settings. This is more conventional when it comes to using a product. Also, I would place a handprint on the part that you are supposed to open to graphically demonstrate how one is supposed to add water.