In real life, arrows and bullets are surprisingly ineffective at actually making people physically stagger. Hollywood likes to tell us otherwise, but Hollywood doesn't sell reality. People who are hit with bullets sometimes don't even realize they have been hit until they see the blood or experience pain while moving. An arrow stuck in you is harder to miss, but arrows really don't cause much trauma to the body. They are finely pointed and pierce the body rather than impacting it. There is too little kinetic transfer between the arrow and the target to cause a person to fall to their knees from being hit. Arrows kill by blood loss mainly, not the force of the arrow striking the target (unless you're hunting birds with a blunt point; there the goal is to crush the bird so it can't fly)
But even though it's not realistic, it looks cool and it's a useful ability in the game.