He is detail oriented. He takes care of every single little detail while writing his code. He sees slightest of deviations between the design and the implementation. He is the kick ass alpha geek in the team.
Attention to detail is a major plus in his professional life and that is a GOOD thing, till the time he starts leading a team as a technical manager.
Then before you know it, he is knit picking on how many days people in his team should be taking time off. Why do you need eight days for a vacation?
He is estimating how many man hours an engineer should take to get a task done because he himself could have done it in a day.
The same attention to detail that makes you an amazing engineer usually ends up making you an amazing asshole when you start managing people.
There are two lessons to learn from this. 1) Before you promote someone and give him a team to work with, measure their ability to detach themselves from the level of detail that they should not be bothered about. 2) When you are working as a technical manager most of the time your ability to trust others, empathize with their problems, helping them out when they are stuck and your ability to provide intrinsic motivation which makes people want to excel and do the right thing is much more important than your attention to every single insignificant piece of information floating around in your universe.
I'm not saying switching attention to detail is essentially always a bad thing. When you are a geek attention to detail comes naturally to you. But when you are managing teams sometimes "actively forgetting" that an Engineer said he was going to check in his code today but ended up taking one extra day to do an awesome job, is also equally important.