A person who wins a game of Scrabble one evening may be late for work because they forgot to set their alarm clock. How could the same person make such a dumb mistake? Call it concentration, or focus, we use more of our brain when engaged and need support when we are distracted.
PDF just a fun reference, the real meat is in the article — nice primer to User-centered Design, so we can “design ways to make [our users] smarter”.
I like that this frames user error as being something that can happen to any of us in a given context. I think that’s a much more accurate description of the way things really are besides just “our users are dumb.” I’ve always chafed against that kind of attitude where people assume it’s just a problem with the users rather than looking inward at how things could be designed better to “nudge” customers toward success.