Being grateful and being complacent are two very different things.
Gratefulness is an appreciation for what you have and an understanding that everything can change. Everything is temporary.
Being complacent is being comfortable, but not in a good way. It's being naive about the fact that you should always be learning and growing. This is a natural human urge that most people suppress until they're just clinging on.
Why would you ever want to be average? Why wouldn't you want to be a powerful owner of your life? A person that makes strong decisions that are good for you.
Remember to never get too comfortable. Push yourself. Push hard.