The thing about investment bubbles is that the irrational exuberance occurs because there is a genuine sense that big things are possible. Since 2010, there has been some sense that an Internet bubble is forming, that expectations are unrealistic. Of course, that is the excessive side of the belief that something big is afoot. We probably have both at the moment: a time when some truly new and big things are coming, and the near certainty that valuations are too rich and that too many firms will be funded.