Or another problem, via this analogy:

Crowded theater, fire starts, everyone runs for the
fire-exit at the same time, and within a few seconds,
all flow has stopped:

Turns out that two really-fat guys happened
to have their right near the door, so they were the
first to get to the fire-exit door -- they hit the
door at the same time, wedge together trying to
get through it, and *no one* gets out of the building!

One solution: keep around a water container, eg a coffee-can,
fill it from the sink or bath, and at exactly the same instant
the fire-alarm goes off (flush-lever is pushed), dump the
whole can-full of water just in front of the exit-door:

that blasts the two fat-guys (all guys & gals, in fact)
out away from the door, out into the room, so that
the people, both fat and thin, will hit the doorway
one at a time, and *everyone* can escape.

David