I've done my fair share of listening to managers (many of whom are former clients) complain about their employees and losing good people, which adversely affects their ability to perform well. 
Diving deeper into their organizations to assess culture and morale and "get the full picture," I've found multiple fingers pointing back at management. Gallup stated it a long time ago: "People don't leave jobs; they leave managers."
That's really where it starts and ends. To whoever is privileged enough to hold a manager's title, the first step is realizing your blind spots in the often neglected soft skills area of leadership. 
Here are five reasons I've seen for good people turning in their resignation letters.

1. Managers displaying extreme emotions.

I speak of bosses who express visible and public anger, yelling across hallways and conference rooms at the drop of a hat, or marching to other departments to "tell someone off" without realizing the fishbowl they work in (yes, people watch, take notes, and many are affected by it).

2. Managers who can't, won't, or don't recognize people for good work.

You do great work. Your peers and colleagues know it, your customers know it -- and your manager ends up taking all the credit. Been there? Worse, managers dismiss the value of their people and see them merely as cogs on a wheel rather than as worthy colleagues hired to perform with excellence. This will suck the life, energy, and motivation straight out of an employee. 

3. Managers who act impulsively.

I speak of the type of manager who steamrolls ahead with important decisions without soliciting input and getting buy-in from team members. They're typically short-sighted and often fly by the seat of their pants. The end result may be burned bridges, decreased trust, low morale, and disengaged workers.

4. Managers who are total control freaks.

The work environment they create is overbearing and stifling because they want control over all decisions. Such managers distrust the team, so tasks rarely get delegated to others. There's hardly room for group discussion or input because the management style is autocratic, which limits creativity and the team's desire to learn new things. 

5. Managers who have ginormous egos.

People in management have egos -- that's a given. Sometimes it's necessary, to an extent. But unhealthy egos running amok are obstacles to success and performance of both the manager and of the team members. You'll see it in action by the amount of time such managers spend protecting their position, status, image or reputation. To them, feedback is deemed a threat to their power and sense of self-worth, especially if it's negative. Great leaders, on the other hand, value truth and honesty and see feedback as a gift to improve upon their leadership so they can serve others and their mission better. Even when feedback is negative, it prompts an exercise in curious exploration to find out where things went wrong so that it doesn't happen again.