Bubble

Economists argue about whether bubbles are the result of irrational crowd behaviour (perhaps coupled with exploitation of the gullible masses by some savvy speculators) or, instead, are the result of rational decisions by people who have only limited information about the fundamental value of an asset and thus for whom it may be quite sensible to assume the market price is sound. Whatever their cause, bubbles do not last forever and often end not with a pop but with a crash.