My family is having a debate right now. We all have different levels of Jewish observance. My mom and I attend Chabad services of which a Minyan is very important. My sister attended services today for Sukkot and Shabbat and we did not have a Minyan. I have been saying Mourner's Kaddish for my grandmother (she does not have living children) and I asked about saying the Mourner's Kaddish for her today. I was told that we can't say the Mourner's Kaddish because we don't have a Minyan present. We had 6 men present.
My sister then argued and asked "why do we need 10? We have more than 1. It seems arbitrary to have to require 10."
We searched online and found the significance of the number 10 but that doesn't answer my sisters question. My sister's argument is essentially we are willing and 'able' to do the prayer so why not do it? Wouldn't doing the prayer be better than not doing the prayer regardless of the number present? I understand certain reasons why one doesn't do prayers alone but we are asking in the case of praying in public with more than 1 person but less than 10 present.