I've read some ideas that indicate physical laws must be involved. In essence: force = mass X resistance, and when Sir Newton is moving, he wants to stay moving. To me this shows that blocking an attack is meeting force with force creating an 'unnatural' situation of twice the force. If resistance is 0, then force becomes 0, and Sir Newton goes right on by as you tenkan (or in some cases flat to his back, face, etc.).
Thomas Jefferson said "In matters of fashion, bend like a reed. In matters of principle, stand like a rock." To me, this epitomizes my Aikido study in that Uke's attack is received and I bend, but I stay in my center, my rock.
The best option in essence is the 'win - win' option where neither nage nor uke is hurt. I know how to hurt, to attack, to apply force. I learn Aikido to respond to those who would attack, and subdue them in a way that negates harm to me and the attack. Now and then if the learning curve is flat, nikyo, sankyo, shiho, higigi, and other 'pain techniques' seem to be effective, but the end result is the same: stop attacking!.
You can't predict the lightning, but you can predict the thunder after the lightning strikes. Uke gets to be lightning, Nage thunder.