system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How the stock market can "crash."
gpt
A lot of stock trading takes place on the "bigger fool" theory.

It may be true that only a fool would buy a certain stock at a certain price, but if a fool buys it and then sells it to a bigger fool at a higher price, he will still make money. So a lot of people take stupid risks on the assumption that they will always be able to find a bigger fool.

Stock prices crash when it appears that they are running out of fools.