A manager of people needs to understand that all people are different. This is not ranking people. He needs to understand that the performance of anyone is governed largely by the system that he works in, the responsibility of management.
The supposition is prevalent the world over that there would be no problems in production or service if only our production workers would do their jobs in the way that they we taught. Pleasant dreams. The workers are handicapped by the system, and the system belongs to the management.
When a system is stable, telling the worker about mistakes is only tampering.
The various segments of the system of profound knowledge proposed here cannot be separated. They interact with each other. Thus, knowledge of psychology is incomplete without knowledge of variation.
A system must be managed. It will not manage itself. Left to themselves in the Western world, components become selfish, competitive. We can not afford the destructive effect of competition.