In a series circuit . . .
There is only one path for current to take.
All the way from one terminal of the power supply, through all of
the lights, computers, vending machines, air conditioners and
everything else in the building, to the other terminal of the electric
supply. One path !
So the current for EVERY device has to flow through ALL of them,
because that's the only path there is.
If any ONE device in the building was turned off, burned out, or
unplugged from the outlet, then there would be NO PATH for the
current, and everything in the building would lose power !
Not a very convenient way to operate a house or a building.