Every man has a weakness. Something they will never conquer (on their own).
That is the entry point. That which you can do, overcome, and handle with ease, whilst this man struggles with. This is your entry point in negotiations.
This is where range is your friend.
The greater your range, the more you can do and be. To master domains.
Sell the dream coming to fruition. The one. That one. The one impossible to achieve on his own. He has weaknesses and skill gaps. He needs you.
Help him escape his misery. Each man has imprisoned himself. Be the one who promises and delivers freedom from his suffering.
He knows it, deep inside, that his inability to achieve, and that his suffering is self-inflicted. He cannot help themselves.
He needs you.
