When cutting, the sword exerts force on the target, and the target exerts force right back on the sword. This force is what causes cuts to be less effective, and possibly fail. And where does it come from?
Even if you don’t like singlestick, there is a lot to learn about how the afterblow affects both the attacker and the defender independently.
From a physics point of view hitting ‘hard’ can be a somewhat difficult property to quantify. Learn a little bit about what can make a strike ‘hard’.