In a bubble, asset prices become disconnected from reasonable expectations of the future earnings of those assets. Markets fail to get prices right. This mis-pricing gets reinforced and exaggerated by herd behaviour, or irrational exuberance. Investors convince themselves that someone else will pay even higher prices for the assets in future.
4  BIS Review 48/2004  In the case of commercial buildings in the 1980s, the pace of construction was frantic, as supply rose to meet the high demand which was manifesting itself in high prices. Anyone who was around at that time can remember the cranes that cluttered the skylines of our major cities.