Managing people can take an entirely different set of skills from knowing your product.
To effectively manage people you certainly need to know the process and what you are asking them to do so working your way up is certainly essential to your success, that said if promoted or if you want to take more on you then have to put yourself in the other person's mind set and skills.
You need to access everyone's positives and work with that, you can not just bark out orders or assume they know what you are asking, it is up to you to explain what you want and why.
The why is crusial for growth, as a leader or manager you have to be a good teacher and most of all you have to care, care about the success of others.
In order to be the best boss, manager and/or teacher you must watch, listen, observe and help.