To add on this. You and a friend are astronauts in space, holding hands. We are a system. Our center of mass is between us. If you push on your friend, no EXTERNAL force acted on the system you + friend, so your center of mass shouldn't change its state of motion. For this to happen, a net force of 0 should happen between you two. Ergo, any force you apply will be reflected back to you.

But then wouldn't stuff never ever move? If forces were always equal to 0? The point is that the system you + friend experience 0 external forces, and no motion. But if you look at the system only friend he experienced an EXTERNAL force (you pushing) And if you look at the system only you, you experience an EXTERNAL force equal to your push reflected.

Each of you moves, but the overall system does not change.