Have you ever been waiting too long for a bus and suddenly two buses appear?
Do you ask yourself why it happens?
Setosa makes possible to understand this and more other things by visual explanations.
Going back to the buses, here is a very simple simulation that lets you play with 2 buses doing the same route.
As you can see from playing around, it is quite easy to destabilize the system but difficult to bring it back to the situation with regular buses. One way of going back to normal is if the second bus stops and waits for the other buss to be quite ahead.
If you like it, then explore other visual explanations.