No is essential
If you believe that you must keep your promises, overdeliver and treat every commitment as though it's an opportunity for a transformation, the only way you can do this is to turn down most opportunities.
No I can't meet with you, no I can't sell it to you at this price, no I can't do this job justice, no I can't come to your party, no I can't help you. I'm sorry, but no, I can't. Not if I want to do the very things that people value my work for.
No is the foundation that we can build our yes on.