#1: The primacy of communication.
Communicating well is one of your most important arts. Large and sustained success come only through others; you reach others only through communication. And since you are ultimately accountable for your own successes, it is your job to be understood.
It is not enough to speak, or write, and expect others to understand. The people you wish to reach lack the time, context, or ownership of your ideas. They hence have little incentive to decipher what you say. To reach them, you must take full responsibility for ensuring your message is understood and remembered.