Do not be complacent about your achievements and not to strive for continual improvement when you get to the top. As soon as you let success go to your head, you sink into following familiar patterns and play it safe. In other words, you risk losing your edge.
The comfort zone is a psychological state in which one feels familiar, safe, at ease, and secure. You never change your life until you step out of your comfort zone; change begins at the end of your comfort zone.