A recent report showed that 59% of managers said 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,” Cappelli says.

And yet, though 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.)

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