Everything was great, except I had some problem with the bath faucet. (Later, I found out one of my colleagues had same problem.)

The faucet looked like this:

(I should have taken a picture…)

It was very clear that the red dot stood for “Warm Water” and the blue one for “Cold Water”.

So, how do I get warm water?

I tried below operation but I failed. It didn’t move.

(This is so-called “User’s Model” *)

And I tried in the direction out of this page. I failed again.

I was very confused. Then I accidentially found it works like this:

(And this is so-called “Design Model” **)

It’s a very good sample that the design is to make it look better but less workable. And the user’s model cannot map to design model very well.

I would think to myself – DON’T HAVE THIS FAUCET IN YOUR SOFTWARE!

*,** – Please refer to the book “The Design Of Everyday Things”, which I was just re-reading on my flight.