The document discusses how the idea that "it should be usable with no training" is not always valid. While sometimes products can be usable without training, there are exceptions in complex domains, for complex tasks, or where errors could be high-risk or dangerous. It provides examples like air traffic control systems, weather forecasting tools, flight simulators, and remote surgical systems to illustrate that training is necessary in some cases to properly understand complex systems or tasks and minimize risks of errors. The key point is that products should aim to require only necessary training rather than addressing usability problems solely through training.