Cicadas chirp to attract mates but the noise can also bring the unwanted attention of predators. That leads to an interesting synchronised behaviour in which the creatures chirp in a coordinated fashion, creating a kind of chorus.
It's not so hard to see why. Cicadas that chirp ahead of the chorus stand out. That makes them more likely to attract a mate but also more likely to be eaten by a predator. However, it turns out there is a best time to chirp, a kind of "sweet spot" in time, that maximises the likelihood of reproductive success while minimising the risk of death. That's what generates the chorus.Humans also demonstrate synchronised behaviour. One of the most interesting examples is in science when a number of individuals often make the same discovery at the same time. The reason is that those who announce their discoveries too early are likely to be condemned as cranks by their peers, while those that are too late have obviously missed the boat.
For some reason lemmings come to mind. So the takeaway here is that if you can get a bunch of suckers to buy the same crappy stocks, the value will go up temporarily. That's pretty much the basis of our modern financial system.