The fear for a real sword.
As practitioners of Iaido, we would eventually arrive at a point where the practice sword (made of Aluminium alloy) grows less and less appealing, some may opt to move to a "Shinken (真剣)" real sword. "When should I move to a real sword," one might ask. There isn't a real answer, given you have had enough practice and that you will not injure yourself each time you draw or re-sheath your sword! This is one reason that many beginners are instructed to repeat these two specific motions over and over until it can be performed like second nature. Be mindful of your surroundings and placement of your own limbs especially fingers, that is if you value all your body parts as I do. You need to be afraid of a real sword, because it demands your utmost respect.