One problem he doesn't account for is that the community of users is often diverse and therefore ui complexity gets driven by corner cases. Often teams will start out with a visionary who holds the line for a while but gradually the pressure to add another bell or whistle increases until it is impossible to resist. For example coversion rates; if a feature is shown to drive up conversions by a small amount it will tend to get added, it doesn't take many of these discoveries to ruin an interface.
In the early stages of a project everyone is a beginner. Success is success because people become experts and experts are experts because they know how to do and want to do sophisticated things.<p>The example of the toilet is perfect. Good interfaces are designed to meet the needs of the user community. An expat in Japan is not a member of the community for some sense of "member" and "community". The solution for the outlying case is that the outsider asks for help. This transfers the expertise.
The biggest challenge is providing all the functionality that users want with a clean UI.<p>There's a trap and tradeoff in making an interface too clean: discoverabilty suffers.<p>Some users might never go beyond the simplest of use cases, but more advanced things need to go beyond that and it shouldn't be hard to find out how.<p>If users have to google how to do something, you have lost.<p>Apple is a good example of this. They value their clean and intuitive interfaces.<p>But I don't think they actually are. Give an iPhone to someone who hasn't used it in a while and see how well they handle things...
"Clearly define a functional happy path for the users' goal."<p>There is never just one functional happy path or goal.<p>Each user is uniq.<p>Even same user expectations and 'happy' path change with time.<p>Take the Airbnb example, yes, at one point you just want to book a new trip.<p>Maybe your looking for the invoice of a past trip?<p>Maybe you are looking for an old booking because a friend is going to that city and you want to recommend it.<p>The more users, the more goals.