"Come," I said, with decision, "we will go back; your health is precious. You are rich, respected, admired, beloved; you are happy, as once I was. You are a man to be missed. For me it is no matter.
It allows him to hear the war drum that forces him to kill. The acute silence makes the narrator so uncomfortable, he must make the old man scream. The narrator thinks that only killing the old man will make all of the surrounding noises disappear
Because they might not explain it clearly or right ,they might go mad if you don't put the answer they told you,and they think their always right.