When a person is demonstrating for an audience how to do something, there are generally unexpected results. Sometimes the demonstration goes according to plan. This in itself is a surprise because it doesn't happen very often. The instructor may have an off day, or the clay might be unworkable for some reason. These errors, mistakes and incidents are very instructive when they occur. They are an illustration of what may happen whenever a person sits down to create a pottery item.
Pottery is a relaxing way to create beautiful objects. It is not often that people think about the mistakes and errors that can push an artist off track when creating them. Even experienced artists have bad days where things go wrong. Learning how to correct these problems is an integral part of the learning process. Real life issues cropping up during a class or demonstration are usually much more helpful than any other learning method.