In my 26 years of professionally working, I’ve seen this time and time again. Even if they don’t leave out of fear, their morale and productivity is drastically affected.
Conversely, when you promote the right people, employees are happy for them and gladly follow them. Even when it’s not them who is promoted.
I used to report to a guy who started as an intern for us, but he was really good and knew his stuff. So as we all moved around and he continued to rise up the ranks, when I was eventually shifted into his world, I didn’t begrudge it. I knew he earned it and I knew how good he was. I welcomed him as a leader, as did the rest of the team. Don’t underestimate how important these dynamics are.