You just got the keys. Now you have ninety days to prove it wasn't a mistake.Nobody hands a new manager a plan. They hand you a set of keys, a schedule with holes in it, a P&L you have never seen before, and a staff that is quietly deciding whether you are worth following.Most new managers spend month one reacting. They fix whatever is loudest, avoid whatever is unfamiliar, and assume the numbers will sort themselves out. By day 60 they are underwater. By d...