Harvard Business School’s mission is to “educate leaders who make a difference in the world.” This motto is vastly more ambitious than the previous one — to educate leaders who “make a decent profit — decently” — and ambition, as Nitin Nohria (now HBS’s Dean) and James Champy wrote in The Arc of Ambition, is usually a valuable quality. The problem with the new mission, though, is that it’s missing one word: positive. Of course, HBS hopes to educate leaders who make a positive difference in the world, but that’s harder to do than it might seem.