But how do we know when irrational exuberance has unduly escalated asset values, which then become subject to unexpected and prolonged contractions as they have in Japan over the past decade?
Francis Boyer Lecture of The American Enterprise Institute for Public Policy Research, Washington, D.C., December 5, 1996
FRB: Speech, Greenspan -- Central banking in a democratic society -- December 5, 1996[federalreserve.gov]