Housing bubble theorists will offer you a list of reasons why it might have been appropriate to have a bit of a housing boom, and then (perhaps correctly) show you that the factors on their list are not big enough to explain all of the housing boom we actually experienced. The final step in their argument is to attribute all of the unexplained part of the housing boom to irrational exuberance.
Of course, the entire argument falls apart if their list is incomplete. For example, do those lists include this?
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American's incredible accumulation of stuff is real (itself caused by China's seizing its comparative advantage in making that stuff), and the accumulation undoubtedly increased American's demand for space at home. The self-storage industry profits from this demand.
Note that I do not claim that the entire housing boom is due to American's demand for closet space. In fact, that's the point: there are any number of things that we may someday understand to explain the residual, and I see no reason why those possibilities are limited to "irrational exuburance."