Because it pushes you to beyond where you're comfortable which in turn encourages growth. Sometimes when you fall flat is when you find the drive to try that much harder.
Life is about growth. Growing allows us to expand the value we receive out of life and the value others get from us. It allows us to move forward in our careers, with our relationships, and seek self-actualization in many areas.
As a hardcore introvert, I completely understand the comfort zone and staying within it's boundaries.
Recently, I was very uncomfortable with life. I was moving around with my husband for his job, living out of hotels. We didn't have very much money. I didn't feel comfortable getting out in new places, seeing new people. All I wanted was to go home where it was comfortable and where I knew everything and everyone.
After about two and a half years, I got what I wanted. I got to go home and live with my parents again, same sleepy little town I love. I got a job working for the same company I worked fore before I moved. I went to the same places, did the same things.
I hated it.
I had grown past it into a new person. I was more confident, more assertive, and I had learned a lot. I realized that I wouldn't give up what I had gained from my experiences to stay where I had been comfortable. My old life stifled me.
Sometimes the comfort-ability we know and cherish turns into exactly the thing that holds us back.
Move beyond comfort into the unknown. Explore and challenge yourself.
Scary things, the things we shy away from but know we should probably do, those are the things that will make us into the people we need to be.
You have dreams. It's terrifying to think about chasing them sometimes. There's so much between you and the end result you crave. What about all the new things you need to learn? What about the people you need to reach out to? What if they don't like you? What if you fail?
Fear is a motivator too.
But perhaps like Steven Pressfield says, it's the compass that points you toward the thing you most need to do.
Do things that scare you. Get comfortable with those things, so you can keep progressing.