The concept is that a worker is really good at their job, so good that they clearly deserve better compensation for all they bring to the company, but business is structured so that the only way to get more money is to be promoted to a higher position. A new position comes with new job requirements, but not everyone is going to be right for those. Example: an amazing computer programmer might be useless at managing staff, but if you promote that programmer to head of the department they’ll be required to manage staff. It seems like the best thing for everyone, the company included, would be to put that employee back in their original job and let them keep the higher salary since they clearly do the job well enough to deserve it. However companies want those lower level jobs to be seen as undesirable so workers will feel upper staff deserve their higher wages. Because of this, putting the employee back in the job they’re right for is considered a demotion, so instead companies let the employee keep the upper level job they’re bad at forever or until they have just cause to fire them. Clearly the company was better off with them in the job they were good at, but the illusion of hierarchy to justify higher waged employees is more important