I have just got to smile and laugh as I read this quote. You can only say something like this if you truly understand that there are lots of things you don't know, or if you are entirely stupid. My guess is that Isaac Asimov was a very wise guy, meaning that this quote actually came from his wisdom.
I remember from my childhood a similar word of wisdom that said: "Those who believe they are finished with learning, are finished."
In other words, if you believe that you have reached the top, it just means that you have reached the finish, not the top. We always need to grow and we always need to stretch to get better and wiser.
Another thing worth learning from this quote is that there are things we can learn from everyone. Even though they might lack knowledge in many areas, everyone has a talent of some sort, and they have wisdom in one area or more. As a result, there are things we can learn from everyone, and if you are hungry for learning and hungry for wisdom, you can always learn every day and in every situation.