[TwistedWeasel]

The hard part for me was that managing engineers takes a lot of time and energy, it's not possible to be a full time engineer and a full time manager.

Over time your understanding of the technical details of the work your team is doing will atrophy and where once you may have been an expert on all aspects of the system you must now rely on the judgement of the senior members of your team when making decisions. This is hard for a lot of people, to know that you don't know enough to make a decision and then to trust your team enough to help you make the right one.

Building that trust is important, because without it you'll make bad (or at least uninformed) technical decisions. it's easier if you moved up into a managerial role from a team you worked on instead of being hired to manage a team you just met.