To become whole, accept your defects.
When you accept your defects, you then have none.
Still, if you think you have no defects, you are not whole.
Let me expand that ...
As you evolve, you get the (somewhat justified) feeling you can do more. You also get the feeling that you're better than before, superior somehow (which in turn is not justified).
Then, you start telling yourself you're a new person, and forget that all the problems you've been having are actually still there, and in the end, you become ... infatuated (?) with yourself.
Or, of course, you can stop all that, by simply remembering your 'darkness', remembering that you still bring all your defects and problems, that in the end, you're nothing special.
So, you have to, on one side accept yourself as you are ("dark side" and all) and see yourself as both "dark" and "light" at the same time.
I guess that's, in the end, the meaning of the tao circle.