I really think it takes a combination of good technical skill, ability to manage and encourage staff and delegate work appropriately, the ability to appease the client, and an eye towards marketing.
It's not easy and those aren't always skills that go hand in hand.
I'm still new and inexperienced enough where I'm not managing projects yet, but in the past few months or so (aka since I got licensed) I've been a "task manager" on a number of aspects of projects.
By that I mean being in charge of completing a particular part of an overall project, answerin directly to the PM.
It's been a challenge to say the least. Handling the CAD, survey, admin stuff, etc. Handling the people and keeping the work going smoothly is easily as difficult as the technical side. At least with the design, there's a book that tells you what numbers to use.