I often refer to the Evil E’s. I started using this term to refer to behaviors in people that were destructive to a team. The Evil E’s are: Ego, Envy and Entitlement. Let’s start with Ego.
 
Everyone has an Ego; it’s natural and necessary, but it can grow out-of-control. When it causes a person to stop acting in the best interest of the team, it’s one of the most destructive, dysfunctional behaviors possible. People with a destructive Ego will often display the following three behaviors:

1.) An inability to listen to any idea other than their own. They lock in on their opinion. Even worse, they will jump into a situation and undermine others because the decision was not theirs. Making the “right” decision is less important than making sure it’s “their” decision. They slow down innovation and progress to make sure they have made their mark. They talk about needing to control resources, but avoid accountability.This behavior drives out other strong teammates who do not want to be dominated and want to be heard. This behavior also stifles the voice and drive of the teammates who stay, reducing the brainpower and effort working to make the team great.  The net effect is a lack of trust, a talent drain, fewer ideas, and even fewer vetted ideas. 

2.) A need for individual validation all the time. A person with an Ego issue will take credit for the work or ideas of others, even in their own head. Often times, the word “I” will be used when they talk instead of “we.” People work “for” them, not “with” them. Title, office size and location are more important than their job and teammates.  The fixation is on themselves over the good of the company, team and clients. This blatant self-interest destroys the trust of teammates who start watching their own backs out of a survival instinct.  The effect is always to have a team that is not working together very well.
3.) They feel they know it all already.  In every area, they think they know all they need to know. To them, training is a waste of time.  This excessive confidence means they stop learning new things.  No matter how much talent or ability they had at one time, they do not evolve and improve like the humble folks who love to learn. The end result: the ability gap between the egomaniac and the hard-working humble person grows so much over time that the person with the excessive ego becomes obsolete (yet they don’t know it).
So, look out for signs of your own Ego getting out of control. In my office, I have a photo of my grandfather being treated like a king (he was in the military in a foreign country). He inspired me to work hard, but I also can see how easy it can be to become egotistical.  This is my reminder to stay humble.

Beware of the person with Ego when building a team, no matter how good they look on paper.  Due to the nature of a person with Ego, either due to extreme unjustified cockiness or their innate insecurity, I’ve found it’s a very hard trait to change in people. The behavior will invariably take a lot of effort to manage and will make building a cohesive and high performance team very difficult.