Having a Thick Skin allows you to take advice. It allows you to listen to people that give you input prior to publication. This includes editors, beta readers and even writers groups.
I have seen writers that are totally UNABLE to listen to criticism. They cannot stand for anyone to say their baby is ugly.
If you can understand that every first draft is crap, share your work, listen, filter through the advice, act on the feedback, your story will be better. Even when you are done, it's been professionally edited, you are not done.
I always print several, "Red Pen Proofs" and have people read it and literally red pen it.
Having a Thick Skin will make all this work easier.
After your book is published a Thick Skin is also handy. Reviews are just the start. Readers will also email you. Critics will write about you. Your family won't take the time to read your book.