Lets say that you own x units of item y. You sell one of item y to someone for $100 dollars on an established exchange. According to the exchange, you have 100*(x-1) dollars of wealth.
Next day, some person comes along and tries to sell the same item for $100, but can only find a buyer for $50. Your wealth has now been cut in half.
Thus the challenge is separating market feedback reactions (aka fear and bidding robots) from real-world valuation adjustments (aka mere delayed demand vs. destruction of long-term value).
I think the old George Carlin quote applies perfectly to it - "Think of how stupid the average person is, and realize half of them are stupider than that."
If you've ever tried to pick stocks, you'll see countless examples where the stock price just seems to ignore the realities of a company. Level Three Communications taught me that lesson. Huge backbone fiber provider, growing and scoring major contracts continually, increasing revenues/profits for a decade, and the stock prices was practically constant. Then they rebrand as a CDN (with zero impact to how they operate) and their price rides the buzzword wave right into a big acquisition.
So the market price isn't as real or as much of a consensus as people think it is. If you average a lot of opinions, the result isn't necessarily anyone's opinion, much less a correct one.