Consider the firing of a cannon. Before the fuse is lit, the total momentum of the system (the cannon and the cannonball) is zero. Both are stationary. When the cannon fires, the cannonball hurtles forward with tremendous speed. It has gained "forward" momentum. But the law dictates the total momentum must remain zero. Therefore, the cannon must gain an equal amount of "backward" momentum. It lurches backward in a violent recoil. The cannon didn't "choose" to move back; it was compelled to do so to balance the cosmic equation. The action of the ball flying forward necessitated the reaction of the cannon flying backward to ensure the total momentum of the system remained unchanged.
She ordered the crew to the forward cargo lock. Six of them, in suits, grunting and sweating in zero-G, unbolted the batteries one by one. Each battery was a chunk of potential momentum. action reaction and momentum conservation
If you push forward, the reaction force pushes backward. Consider the firing of a cannon