The following article was originally published by Wharton Executive Education.

A recent report showed that 59% of managers said that they had received no training on how to be a manager before becoming one. Management professor and director of Wharton’s Center for Human Resources Peter Cappelli says that stunning statistic is compounded by the fact that most of those managers are now supervising people who were their peers before they were promoted.

“Research tells us that the individual contributors who get promoted — those who are the highest performing when it comes to their individual role — make terrible managers. It’s not just that they’re not good — they’re the worst.”

And yet although the practice (and its poor results) is common across industries, few companies and individual managers figure out why the fail rate is so high (hint: the new role requires completely different skills and behaviors). “To be a good individual contributor,” Cappelli says, “you must think about yourself, your performance, and how you can improve. But once you are a supervisor, you need to think about how to help other people do well. You can’t just expect people to make that kind of change on their own.”

Cappelli says in addition to recognizing that what got you promoted isn’t what you need to succeed in your new role, there are three other common reasons why new managers struggle. The good news? They all involve skills that can be learned.

1. Accept That Social Relationships Have to Change

Not everyone is delighted that you got promoted. Some of your new subordinates may have believed they were in line for management, were better suited for the role, or otherwise resent the advancement. “You have to recognize that your relationships with your former peers have to change,” says Cappelli, “and changes are often unpleasant.”

Specifically, he says the belief that a manager can be the boss in the office and switch into friend mode at the end of the work day is “a division that’s impossible to sustain. It’s the reason why in organizations like the military, where the bosses are in charge of putting people in harm’s way, they don’t even want officers socializing with their direct reports. Problems arise when authority becomes clouded by personal relationships, and that’s just as true in the office. Our MBA students are often surprised by this, thinking that the job of a supervisor is to be a friend to your subordinates. It’s not.”

“Research tells us that the individual contributors who get promoted … make terrible managers.”— Peter Cappelli

Cappelli says although the role of manager has evolved from the “ruler of the office who doesn’t have to worry about the subordinates” to a more collaborative and even compassionate leader, it doesn’t mean managers and their direct reports are on the same level. “One way you might discover that is when you become a supervisor and you don’t get invited to happy hour anymore.”

“Happy hours with your coworkers generally involve complaining about your bosses. So if you are the manager and you get invited, you should go. But be prepared to buy the first drinks and then go home. They don’t want you there. Even though you may feel you’re still buddies with these people, the relationship has changed — a lot.”

The bottom line is pretending nothing has changed doesn’t work. “You might think it doesn’t matter. But what about when somebody comes in late. Do they feel the need to tell their peer why they’re late? No. But they should tell their supervisor, and if they still think of you as a peer, they might not. Instead, they might expect that you will overlook it. Those kinds of issues can be very difficult to manage.”

2. Clearly Communicate Expectations

Cappelli says managers can better engage their subordinates by making it very clear who is responsible for what, emphasizing that they are partners with different roles. “This is good advice all the time, but in the transition from individual contributor to manager it is even more important because your direct reports will probably test you in some ways or watch you to see whether you’re going to be a buddy or a tyrant. Rather than making them guess by observation, you should tell them what your model is.”

He suggests that managers should explain that it’s their job to deal with the people above them, and to report on behalf of the team or the group. They should also communicate that they are not going to micromanage their subordinates. “It’s very important to convey that you assume everyone will get their job done, and if they run into a problem, they will come to you to help solve it.”

“You’re not employed as a friend or a therapist.”— Peter Cappelli

It’s also vital for managers, who are charged with managing others’ performance, to give “objective feedback as often and as early as possible. Most employees think they’re doing far better than everybody else, which of course is statistically impossible. This overconfidence becomes a bigger problem when you have to step in and let them know that their performance is average or there’s an issue. It’s easier for them to blame you than it is to readjust their whole worldview. As soon as you get in there, talk about performance issues, and help them understand where things need to go as you move forward.”

3. Maintain Boundaries

Another area of difficulty for new managers is setting boundaries with direct reports who were peers. They probably think that you will tell them everything if they ask you a question, especially if one team member complains to the new manager and the other team members want to know about it. “There are a lot of things you can’t tell people, and the sooner they find that out, the better. Make it clear that you have an obligation in your new role to maintain confidentiality. It might be hard to say, but once you do it solves a problem. People probably know it, but it’s better to remind them — quickly.”

Boundaries are also critical if you have a subordinate who is struggling with performance or motivation issues. If those problems are caused by the workplace, you can look at the tasks they perform, misunderstandings or knowledge gaps they might face, or understanding about incentives and other things within your control. But, says Cappelli, don’t try to debate them into performing better. “It won’t work. They can and probably already have rationalized the issue. You won’t win.”

But what if the problem is outside the scope of work? While it’s common for new managers to try to help solve it, Cappelli says to resist the impulse. “You’re not employed as a friend or a therapist. You’re employed as a supervisor, and there are resources that you can direct them to, but there’s a lot that you can’t do and that your employer doesn’t want you doing. The reality is your advice or suggestions can actually make things worse. And trying to fix someone’s life problems can take up most of your time, every day. Plus, being a supervisor with formal authority over people comes with legal obligations, one of which is the duty of care. That means you shouldn’t put someone in harm’s way. The big lesson here is knowing when to bring in people who know more about this stuff than you do, like HR — and that’s almost always sooner than you think.”

Additional Resource

Peter Cappelli is academic director of the Wharton Executive Education program People Management for Emerging LeadersLearn more here.