Just because you are successful doesn't mean you should stop learning. You should review your learning needs regularly to ensure that you keep your skills up to date and develop any new ones required for your job.
Learning doesn't mean you have to go back to college or attend seminars or conferences. If you have the urge to learn and the hunger to keep your skills honed, here are a few pointers:
1. Learn from experience.
2. Learn from your problems.
3. Learn from your mistakes.
4. Learn by asking questions.
5. Learn from others.
6. Learn by teaching.
7. Learn from your faults.
8. Learn from criticism.
9. Learn how to change your mind.
10. Variety is the spice of life.
11. Seek the truth.
As Lloyd Alexander says "We learn more by looking for the answer to a question and not finding it than we do from learning the answer itself."