Good leaders MUST be good followers. All to often people will get drunk on the idea of "being in charge" and forget that they're still part of a larger team. I've seen teams work on projects that are completely counterproductive to the objectives of the larger organization. You are a piss poor leader if you do not follow your leader.
Without followers you are not a leader. You might be "in-charge", but that doesn't necessarily make you a leader. Many folks make the mistake of assuming that having their name at the top of the org chart makes them the leader. This is not so and is a myth that should be dispelled.
Good followers are not necessarily good leaders. Perhaps the best example of the peter principle at work is to have people try and "groom" good followers into becoming good leaders. While this may work in some situations, there are people who are perfectly happy to follow and not take on the responsibility of leadership.
EGO will make folks bad followers AND bad leaders. The fact that a leader-follower relationship exists should imply that there is a team with shared objectives. When you are on a team, you must check your ego at the door, it's not about you, it's about the team.