You've reached the top of your field or mastered a skill or an art that you're proud of. Don't get too comfortable, though.
The quote above, from Futurice, is a reminder not to rest on your laurels. It's great to be an expert at something, but sometimes that can keep you stagnant as well if you're not careful. It's the whole "Don't rest on your laurels" thing.
Futurice has gathered a series of proverbs like the one above, many of them specifically about programming (for example, "Elegant, efficient, and effective code beats any argument" and "Write code accessible to other programmers. Write code that teaches them"). Others that can be more universally applied ("Being a generalist can be an excuse for not learning deeply.")
Every once in a while we should push out of our comfort zones.