The most consequential assumption behind all his work is that even if human error is to blame, it is hard to imagine any human not making these errors. Humans might fail-but they are not wrong. And if you try to mirror their thinking a little, even the stupidest and strangest things that people do have their own indelible logic. You have to know why people behave as they do and design around their foibles and limitations, rather than some ideal. His great insight was that no matter how complex the technology, or how familiar, our expectations for it remain the same. Norman's discipline, cognitive psychology, wasn't so much about the nuances of buttons and control panels-though there's plenty of that, if you want to look-but rather the ways in which humans assume their environment should work, how they learn about it, how they make sense of it. This is what you have to understand if you are to design an app that people can use the first time they try it, or a plane that humans won't crash, or a nuclear reactor that humans can't cause to melt through the continental shelf.
All these lessons might have remained the obscure province of professors and anonymous designers and engineers if not for a coming wave of technological change: the profusion of computers and electrical gadgets in our everyday lives, driven by the rise of cheap transistors and silicon. Starting in the 1980s, the complex problems you might have found at Three Mile Island became consumer problems, having to do with making buttons work on gadgets such as VCRs and computers, the nuances of designing such devices went on to be expressed in the smartphone. It's no surprise then that the reasons a bad app drives you crazy have a direct relationship to the reasons that Three Mile Island almost melted into the earth. The problems that caused Three Mile Island are similar to the ones that frustrate you when you're trying to turn off the notifications on your smartphone; the inscrutability of a poorly designed light switch shares the same cause as your inscrutable cable box: a button that seems misplaced, a pop-up message that vanishes before you can figure out what it means, the sense that you did something but you don't know what. The presiding notion that you don't know how something works.
It was perhaps only natural that as the smartphone came to take over our everyday lives, the principles that had created it would come to seem like the answers not just to problems of the moment (How do I get people to understand this app?) but to problems of the era (How do I get people to understand their health care?). It made perfect sense if you believed that all these problems came down to the way that the machines failed the people who used them-and knowing that those failures revealed a truth about how people made sense of the world around them, and how they expected the artifacts of everyday life to behave.