You cannot step twice into the same river. – Heraclitus
Achieving success can have the terrible effect of causing you to think that you can reproduce it. But just as soon as you find a way to do something faster/cheaper/better, that idea is now in the world for everyone to borrow/copy/steal.
Simply continuing to do what you did, how you did it, will not be enough to outpace those who learned and adapted in response to your success.
If you are not constantly pushing toward the next innovation, you will soon be losing out to the person who is.