Just as there are stages of accomplishment in learning a skill, craft or trade, there are levels of expertise within those stages. Today, many things about the trades are changing and adapting to newer materials, equipment and techniques. Training, likewise, has morphed in the past twenty or so years into areas of specialization within areas of specialization. Teaching, and learning, an entire trade has been slowly replaced by teaching, and learning, only enough of the trade tasks and skills

Source: https://www.contractormag.com/schwartz/understanding-diagnostics