My experience suggests that in most cases, this does not have to be. I have seen managers reach their "level of incompetence," rethink the situation, then negotiate a new position which carries them beyond where they were. When someone is to be promoted, I think it is incumbent on two people to safeguard against the Peter Principle: The person to be promoted, and the manager who is offering the promotion. Let's look at the subject from the view point of the person to be promoted. (The employer's perspective is discussed elsewhere.)
When the boss offers us a promotion, an ingrained reaction causes most of us to snap to, say "Yes, sir," and accept.
There is something of an ego reaction in it: Our work has finally been recognized, and besides that, we'll get more money. And we quiet the stab of fear within us by telling ourselves that the boss must be right or he wouldn't have offered the promotion.
After all, he knows us and the company so well. (I recall a client who expressed disbelief at the thought that his former boss, the president of a company, could possibly suffer from the common human problems of stress, fear, anxiety, and lack of objectivity.)
If you have been offered a promotion, you should, as objectively as possible, answer a number of pertinent questions:
Is the promotion within the scope of your own career objectives? If it is, fine, proceed to the next question. If it is not, then isn't it time to determine what your next step should be? Can the promotion serve as a temporary stepping stone to the next valid career level, or would it be a setback?
Are you ready for the promotion, and do you have the necessary talent and experience to handle the new responsibilities effectively? If yes, go to the next question. If not, it would be unwise to accept the promotion. If you are uncertain, then it would be a good idea to retain professional help, or (in special circumstances) discuss the matter openly with the boss in order to settle your mind. It would be a shame to refuse a promotion simply out of fear. Oftentimes it can be enough to have a clear description of the new responsibilities by the boss, to discuss those responsibilities with the outgoing manager, and to have some talks with members of that department.
Does the promotion include all the elements necessary to meet your and the company's (employer's) needs? What is the nature of the new responsibilities, and will you have the requisite authority to fulfill them? Or will you be required to seek approval even for less important matters? What problems did your predecessor have, and how can you be sure that you will not have the same ones? Do you have the authority (and the budget) to hire necessary personnel and to terminate those who are not doing their jobs? Is the salary and other compensation appropriate to the level of your responsibility and the contribution you will make? Even if it is, should you not (professionally) negotiate for additional compensation?
What kind of training or other preparation can the employer provide to accelerate your adjustment to your new responsibilities? Is there a specific kind of help you can request? Have you given thought to the habit patterns you have developed in previous jobs and how they might make your transition more difficult? Have you thought about the new relationships you will have, both with the people you have known and with new subordinates? How will you deal with those who, for years, have been co-workers and fiends? (So often friendships are strained and even destroyed when someone is promoted. Sadly, in most cases it need not have happened had there been sufficient prior reflection and effective communication.)
What about your management style in the new position? Good communication skills will make the transition easier. No matter how competent, any newly promoted manager has lots to learn about how things work in the new position. A savvy manager candidly admits that he or she is in a learning mode and then seeks out each subordinate individually to ask for suggestions. Our experience shows that very few bosses do this. Instead, they tend to immediately start making changes and issuing orders, alienating subordinates in the process.
Perhaps it can be a consolation to many to say that nearly 100 percent of newly promoted employees stumble to some degree. Minor stumbles are usually covered up, and the person grows into his or her new responsibilities, over time developing a style that is appropriate for the new position. But all too often, a newly promoted person stumbles so badly or so frequently that the repercussions are more serious - demotion or even losing the job. When we effectively learn to take charge of our own careers, we will take the positive steps required to ensure that this will not happen.