There are more bubbles floating around the earth today than I have noticed in my entire career. Bubbles begin with legitimate economic opportunity but end up crowding out legitmate functions and market signals, resulting in all sorts of distortions and misallocations of resources. They start harmlessly enough where opportunity exists, for where opportunity exists, investment is attracted to capture a return.
A bubble happens when capital overpopulates an opportunity and drives its trading value higher than its fundamental economic value. Since all deviations from reality are at some point rationalized, we can watch at some distance, the natural cycle of a bubble from formation to bursting in a dozen or more on-going markets but some of them we are caught up in more directly.