Every post tends to be occupied by an employee incompetent to execute its duties.
The Executive's & Entrepreneur's Magazine
Managing the Life of Your Business and the Business of Your Life
Every post tends to be occupied by an employee incompetent to execute its duties.
The Executive's & Entrepreneur's Magazine 
The most important implication of your quote, from the Peter Principle, is that someone hired or promoted that person into the position. Given the opportunity everyone rises to their level of incompetency. As leaders we want to ensure we do not set good people up for failure. Over the years I have seen good people damaged because the leaders they depended upon hung them out to dry. Hiring a person is a small piece of bringing them into a position. Hiring must be followed by a strong orientation, Continuing Education and great coaching. People fail because we let them.