Jovictor
We always see people getting reality marbles but never the repercussions. A reality marbles is literally insanity made real. Shiro's works because he wholeheartedly believes that he is a sword. He is not human but a sword in his mind, so all things are swords. Getting two reality marbles would split his mind or invalidate them, you can believe everything is a sword and believe they aren't at the same time.