In the short term it’s a voting machine, in the long term it’s a weighing machine (Ben Graham).

The current episode of irrational exuberance will pass, as others have.

The before ones have had outside influence which forces the irrational episodes to pass. A spectacular collapse is usually fallowed by mass protests and labor actions, strikes etc. which forces the market to change its behavior. Most of the time these will result in a change in government policy which imposes regulation onto the market, and only then does the market go back to being rational.