Never be content. One of my favorite professors told me that. Once you're content with your work, you stop growing.
You're never too old to learn new things. You're never too brilliant to learn new things. If you stop trying to grow, you'll stay stuck and ignorant.
If you're an artist or a writer, you need to use reference and research your work. Fantasy and made-up worlds need to be believable, and to be believable, they need to be rooted in reality. If you have strong work, it could always be stronger. Never stop trying to improve.
Just my 2 cents.
NEVER STOP LEARNING and the world will always be new and wondrous and exciting.