This example I encountered when visiting friends who offered me a cup of tea. As always, I was delighted. Even more because of the teapot they used (see Fig.). No doubt with the purpose of preventing the top from falling off when poring tea, the top had two additional features. First, as a common solution to this problem, on one part of the inside the top had a small lip. In addition, as a second feature, the rim was a bit oval to make sure that, unless it was in the absolute correct orientation, it would not fall out. Although this prevents the top from accidentally falling out, at also makes it virtually impossible to take the top off intentionally. Especially, as the outsider was perfectly circular. Like a professional safe-cracker, you have to slowly turn the top and try if it comes off. The teapot does not present its action possibilities in such a way that the user is assisted in the simple task of removing the top.
This example is almost as bad as the round Apple mouse, delivered with the first iMac series. Not quite as bad, but almost.
See workshop handout chapter 2.