Norman argues for user-centered design (of anything), as it is human to err and designers should always strive to limit the range of errors possible. With this Containment Policy regard for human fallibility, he lays out his understanding of the basic theory behind humans and their interactions with their environment.
As haphazardly programmed thinking machines, our interactions with the world around us can be quite humorous (just think of someone walking into a door). The first question is why did the door not open? Was it a pull the door instead of a push the door situation? If so, why didn't the person realize that? Were there not enough hints? Norman argues that if pushing is needed, only have a flat panel, as it's really difficult to do anything but push. And if pulling is needed, put a large obvious vertical handle on door.
Intrinsic to the above door example is the notion that humans operate in an iterative manner consisting of:
Of course, the door could just be broken, but regardless, this book is an enjoyable topical read which luckily contains pointers to more illuminating readings.