#1 - Managers often have two or three skillsets more fully developed than "management": creativity, intelligence, and dedication do not evenly compensate for a lack of experience managing successful teams and projects.
#2 - You must self-regulate and set personal boundaries on work. Fast-paced pushes and long hours to meet irregular deadlines are a common occurrence. Many projects inspire that sort of work cycle because the team is passionate about the project, and (speaking for myself) I have never received a demand to overwork myself in service of a deliverable, but it has certainly been encouraged. Work patterns ebb and flow.
#3 - The principal, and his role, take some getting used to. His input is crucial to the success of all the company's best output, but some aspects of the project lifecycle can feel punishing and can catch you off guard until you are in tune with his communication style, both what to expect from him and what you are expected to bring to him.