Oh dear, oh dear, must I explain everything for you, Jonboy? I will try anyway.

What Van Goethe meant was our strength can also be our weakness (defect), and our weakness can also be our strength.

For example, you are stubborn as a mule. That is no good right? But on another occasion, because of your stubbornness, you refuse to give up, and in the end you succeeded. So, what was originally your defect is now your strength.

Another example. You are a very kind man. You like to help people. That's your strength right? Now, because of your kindness, people walk all over you taking advantage of you. And yet, you knowingly let them. So, now your strength is your weakness.

Just a couple of simple examples that came to mind. You understand now?