Because a company’s stock price is in theory what the market expects is the sum of the total future discounted cash flows that unit of “equity” generates. [1] This means that fundamentally, stocks are forward looking several decades and beyond. The economy right now might be bad but if the expectation is that there is a slow and long recovery lasting 2 years, if a company is expected to be operational, profitable and…
Does this also mean that the market fundamentally thought, during the Global Financial Crisis, that the sum of the total future discounted cash flows permanently fell significantly? I'd like to see how this concept would explain 2008. If it can, it further strengthens the thesis.
The other part, and this took me forever to realize, is how much "expectation" matters, in the sense of information. If on Monday, I flip a fair coin to decide whether or not to dissolve my business, and then tell you what the coin landed on on Wednesday, then the amount you'll pay for a share in my company on Tuesday is going to be incredibly different from what you'll pay Thursday. Noting for the business changed between those days. Only your perception changed, but it's insanely important. That's a reason swings can happen so near-instantly. The company's finances don't change that quickly, but the information available to investors does change that quickly (like on an earnings call, or after the release of an investigative report).
So in 2008, the near future was weighted heavily and not rosy ("intrinsic" values go down), while investors realized they'd been wrong about their expectations (market prices go down further).