Every investor/trader in stock markets want to be richer than his/her closest rival. That intense greed to outdo each other in this intense battle often lead to irrational exhuberance in the assets that they are struggling for and hence can take their valuations beyond imaginations, and that too within a very short span of time. As long as this intense greed keeps on rising with every passing moment, stocks will continue to remain expensive and volatile as compared to other assets. There has to be some corrective phase in order to restore sanity in the average investor/trader's mind. Who knows what can cause that corrective phase, but when it happens, it will be very painful for all the market participants.