Do you have in-groups and out-groups in your work team? In-groups are those with whom the group leader is most comfortable, while out-group members seem to live on the periphery of the leader's world.
On the one hand, as a leader I know I prefer to work with people who are self-motivated, who are willing to disagree and to do so agreeably, whose work quality is consistenly high, and who either do what is asked or explain why they shouldn't do what is asked. And those not fitting that profile? They end up in the out-group.
On the other hand, there are risks when some members of the group have the leader's ear and others have less influence: good ideas get lost and perceptions of (or actual) biases lead to active disengagement. The full work-group's potential is reduced.
So, is that just the way it is? Because some people, no matter how hard a leader tries to coach a poor performer or communicator, will not get to the level that others achieve we will always have in- and out-groups?
When I teach leaders to coach their employees, I encourage them to focus their energies on those with the greatest potential to improve: taking a B-quality employee to A-quality is like mining gold. Getting a D-quality employee to a C? Well, then you still have a C-quality employee -- what good is that? And at what level of effort and investment of time?
What if the leader eliminates lower-performing employees? Then there won't be out-groups, right? Unfortunately, I see in-groups and out-groups even when employees are working at a high level.
What happens is that leaders, like all humans, are more comfortable with some personality types than others. I might like to talk about my kids but you might like to talk football. I might be into technology and want to show off my latest app, and you might find such talk tedious or vapid.
If you're the leader, TOO BAD! It's up to you to be sure to eat lunch with a variety or employees, take care not to have coffee with the same 1 - 3 people every day, stop by everyone's work space on a regular basis, ensure employees are communicating with each other consistently, and generally be on a friendly basis with everyone equally. Take care to allocate the most visible projects and juicy challenges equitably. Talk up and support all employees when communicating with the higher ups. Close friends are for outside of work.
A leader will make decision-errors if he hears more information or gives more credence to information from his in-group. Take extra care to disband in- and out-groups at work.