How much would your life change, if you changed your thinking?

I ask this question because I started reading a book titled “How successful people think” in which below it says “Change your thinking, change your life” Typically don’t care for books of this type if you will. For whatever reason I thought what the heck, why not? What is it going to hurt?

After going through and answering the questions and journal parts of it, I was struck by how true it really is. Your thinking is a massive part of your life.

If you were to change your thinking how would change your life? Do you believe people can truly change the way they think? How long does it take to expand one’s thinking?