 My paper is about how and why we should regulate the financial system to prevent financial crises. There are kind of two views about this. One of them is that the financial system and banks know the risks that they are taking, but decide to take them anyway because they don't fully internalize the social costs of their actions. For example, when banks are too big to fail, they might not really worry about the downside of the risks that they are taking. Another view, which is historically very popular, is that banks in the worst credit booms don't really know what risks they are taking. They are understating the risks or neglecting it. My paper is about how policy should work in that world, in a world with exuberance. And the lessons are a little bit different from what we know about the other world with too big to fail, because if it's too big to fail, if that's a problem, then we want to really crank up capital requirements in a boom because that gives banks skin in the game, it gives them the right incentives. I show in the paper that when the problem is exuberance, the right policy is not necessarily the same thing. It's not necessarily a good idea to lean against the wind in a boom when banks are exuberant.