Grow a thick skin!
This is the worst writing advice ever, and is a strong contender for the worst life advice ever also.
Because as a painter needs to be sensitive to light, and a musician to sound, and a chef to taste, so does a writer need to be sensitive to emotions. That is what he or she conveys on the page as an essential part of imitating human nature.
A thick skin will stand in the way of what feeds the writer's art.
God preserve me from ever developing callouses on my heart!