wo people push on the same door from opposite sides as shown.

A man pushes on a door from the left. A woman pushes on the door from the right.
They will only see the door move when

both people exert the same force so that the forces are unbalanced.
neither person exerts a force on the door so that the net force is zero.
one person exerts more force than the other so that the forces are unbalanced.
both people exert the same force so that the forces are balanced.