"It's what we think we already know, that often prevents us from learning"- Claude Bernard
we keep learning and learning, that we feel that we already know enough!
The internet has tough us a big lesson: the more you think you know, the more you will find that huge amount of information for the same topic you were learning about is accessible and you didn't know it exist!
Earlier, learning was limited to school and what we read in books or encyclopedia, before the TV was "born"; Nowadays, with the wide access to all kind of information, we realize that this quote is so realistic.
Indeed, we shouldn't stop learning at any point of time!