The sins I perceive when I'm in a leadership position are:
1) Incompetence.
2) Selfishness+deceit
3) Disrespecting authority
1) Goes without saying. There is nothing that can be done when someone is simply incompetent. They need to go, and they need to be replaced, as soon as possible. Showing pity, mercy or good will to incompetent people makes you a trash team leader. You are sacrificing the team's goal, which is your responsibility to achieve, just to satiate some need for being "nice" or "just". It is not just to spit in the face of non-incompetent people by having them tolerate incompetent ones. Recruiting incompetent people is something that hurts you in the long run a lot. Incompetence is not the same as lacking aptitude. Aptitude can be gained, however, there is no cure for incompetence.
2) This is horrible for achieving the team's goal. You have a team, the team has a goal. Every member of that team joined because they have a goal of their own. It should largely overlap with the team's goal, however, this is not always the case. Some people believe they're so god damn speshiul, and so god damn smart, that they can get away with being in the team, and gain the benefits from being in the team, while at the same time blindly chasing their own selfish agenda. I view those people as worms that need to be squashed into obeying. It's extremely frustrating, because they are most of the time, not incompetent, far from it. Usually they're really skilled. You want people with their skillset in your team. You just have to be very careful with them. They're backstabby and will leave when things go south, they're entitled and will not help out on their own, even if they have the capacity to understand that they should, for the team's sake.
It is your responsibility to keep those types in check. Do not allow them to be scum. Act tyrannical with them, and scare them into submission with draconical measures. This is the only language those elite trashes understand.
3) This is not a sin I'm finding out of narcissism. On the contrary. Personally I love having my ideas challenged, and having a constructive discussion that leads to the best outcome for the team. However. The people that do this by disrespecting authority are subversive, and undermine your power. If you allow those people to disrespect authority without repercussion, the people guilty of sin 2) will start running free, like worms on a dead body. Those that challenge authority, are directly detrimental to achieving the team's goal, because they lessen your power. For this reason, it is crucial to punish disrespectful behaviour, even if that behaviour helped with the team's goal. It's unfortunate. If a talented individual did this disrespecting, you don't want him gone, but you want him to understand exactly that his suggestions are valued, only if they're presented in a respectful way, preferably in private, not in from of the entire team. The talented individual might not take kindly to this. In that case, he becomes a direct threat to the team's goals and must be regrettably removed.
Give me a team of humble mediocre people that listen to instructions, and I will tell you, that is the best team I'll ever have, the team of my dreams. Great frustration comes from supervising people. Incompetent selfish pricks that don't see the big picture. Whenever I do it, I get a great amount of disdain for mankind.
That mediocre team, however, depending on the task you've set out to do, is never possible. And probably, results-wise, never desirable. To maximise performance, you'll need so damn many of the people guilty of 2). It's insane. Dealing with them is very frustrating.
I am exaggerating, obviously when I say this. Frustration from dealing with all the above, and managing to deal with everything successfully is the price you have to pay for taking the lion's share.
(don't tell HR about this)