I would wager that very few engineering managers have significant formal training in management. While software engineers can hold a wide variety of degrees, the most common is a CS degree, and few of those include significant coursework specifically about engineering management.

Thus, unlike with IC-track positions, it is likely that an engineer promoted into a management role is coming in cold. And while there are a variety of helpful books and training materials about engineering management, in general new EMs are expected to mostly learn by doing.

“Learn by doing” can be tricky, however, because many of the issues a seasoned engineering manager is expected to be able to capably handle do not happen every day. They happen relatively infrequently, and sometimes only when you change teams, but you need to know how to handle them when they do occur.

Because engineering management is largely a “learn by doing” craft, and because it can take years in the role to experience even the half of what a seasoned EM is typically expected to be able to capably handle, I would argue that the best EMs are those who have had abundant opportunities to learn from their mistakes. But you can certainly speed that up at least a little bit by learning from other people's mistakes instead :)