When you feel something, you heal something and that's how it works. The nature of a human being is to get attached to others feeling and sometimes it works wonderfully and sometimes it's a disaster.
You never know what will hurt someone unless you put yourself in their shoes and try to understand their situation, it so happens that many a time you say something without any wrong intention but it does reflect very badly.
It's a very sensitive thing to make sure you have the right approach to deal with such a situation otherwise you end up spoiling the relationship which takes a lot of time to get built.
No feeling is a stage where you reach when you faced lots of setbacks in life and then you conclude that it doesn't matter to me whatever you say about me, as you do not have any feelings left.