Your first day, your first week in an organization is when you’re observing each detail, figuring out where you stand. That’s when your sense of the culture gets seared in—especially if someone gets stabbed in the neck. That’s when you diagnose the power structure: Who can get things done, and why? What did they do to get in that position? Can you replicate it? At the same time, how you behave on arrival—how other people see you—affects your standing and potential in the company and determines your personal brand.