Imagine there's a place you want to get to along with a lot of other people.
It starts as a nice queue and is pretty orderly but then some people start pushing in and trying to jump ahead in the line. Other people see this and try the same thing. If there's no good exit or crowd control then the back of the crowd slowly pushes against the front until disaster occurs.
People in the back have no idea that there is nowhere to go but they've been standing for hours and want to keep moving forward.
It starts as a nice queue and is pretty orderly but then some people start pushing in and trying to jump ahead in the line. Other people see this and try the same thing. If there's no good exit or crowd control then the back of the crowd slowly pushes against the front until disaster occurs.
People in the back have no idea that there is nowhere to go but they've been standing for hours and want to keep moving forward.