It doesn't always work like that. It's clear to some folks that ZM will decline based on the fact that a COVID vaccine was virtually inevitable. However, there

It doesn't always work like that. It's clear to some folks that ZM will decline based on the fact that a COVID vaccine was virtually inevitable. However, there are lots of investors, mostly retail investors, that are willing to buy a stock without fully pricing that in. E.g. Tim's dad sees that Tim is using Zoom for school and decides it would be a good investment. Other investors are willing to buy ZM for short-term gain as long as they can get out before it crashes back to reality. The same thing happened to Hertz, which even after declaring bankruptcy and almost certainly being worthless continued to trade at a healthy volume. In fact, Hertz tried to get approval to dilute and sell more shares to capitalize off the fact that people were buying their worthless stock.