In light of the Norman reading, this poor design that I encounter every day is the first that came to mind. It may seem like an innocent shower head setup, but it has a sneaky secret than can end up spraying the user in the face via the handheld unit if not careful. The faucet works much like any other shower would, turning the handles to adjust the temperature and pulling up the small bar to switch the flow from the faucet to the shower head. But if the flat knob on the top of the shower head is not pushed down snugly into place, the stream will flow from the handheld unit, straight out at the user and onto the bathroom floor. It may seem simple enough, but the first time I attempted to use it, I received a face full of ice-cold water. As Norman suggests, the designers understand the design perfectly, and therefore see no flaw. If the setup were better designed to give the user the direction necessary to operate the apparatus from the beginning, a rude awakening and the need to mop the bathroom floor could have been avoided.