However, constructive criticism is so helpful! It helps your work grow and get better. It also helps you as a writer grow. You see what people like and what they don't. I think there are many ways to embrace criticism.
DO NOT TAKE IT PERSONALLY! Now this is a hard one. Your book is you. It's your personal work. Don't take it personally. Remove yourself completely from the situation. Don't think of all the time you spent on chapter one which people think should be removed. Take yourself out. This will help you understand the other persons point of view.
BREATHE! Before changing anything in your work, take a moment to breathe. Taking this moment and stepping away will allow you to clear your head and de-stress. You don't want to start editing your book when you're upset. Step away from it for as much time as you need before going back in. When you come back, their criticism won't seem as harsh.
MOVE ON! Figure out whether you are going to use the criticism or not. A big factor in changing your work or not is thinking about whether this is repeat advice or not. If you've heard you have too many run ons five times from five different people, that says a lot. Ask for more advice from other people. Go with your gut! If you really have a feeling you shouldn't change it then don't. It's your piece after all and you can do what you want!
I think the main advice I give you guys about dealing with criticism is to embrace it and go into it with an open mind. They aren't saying things to hurt you. You can only grow from what people critique you on. Take it all in. In the end, it is your work and you can do whatever you want. Just remember, remove your feelings!