I became a manager at the age of 29. It was a big job. I had a lot of autonomy, a good-sized team and no management training whatsoever. And the moment I walked into my fancy new office, my education began.

I’d been working since the age of 11 and I’d had eight bosses by then. All I knew about management was that I wanted to copy the good things I’d seen and avoid the bad. Fortunately, I had a supportive boss and a forgiving team. I made some mistakes, but I learned from them, as I have in every job since.

I went on to manage teams in large media companies like CBS and NBC (while it was owned by both GE and by Comcast) and in tiny Silicon Valley tech startups. I’ve worked in government as well as the service, consumer product, media and technology industries. Though every company was different, the great managers I knew–and there were very few of them–all had something in common: they had very specific personal characteristics that enabled them to be great.

Few people are born with these characteristics, but many more can acquire them if they work at it. These are things nobody talks about, which is a shame because I wish I’d known about them much sooner.

This is my attempt to help other mangers, particularly those who are early in their careers, make fewer mistakes and enjoy long, rewarding, successful management careers.

This book isn’t based on academic studies or on one person’s unusual, one-of-a-kind experience. It’s based on working in the trenches year after year, learning as I went and eventually understanding what it takes to be a great manager.