The author writes about advice he received from persuasion guru Robert Cialdini on the art of favors. Cialdini told him that if you do a favor for someone and they say, "Thanks," don't do what your mom told you to do and say, "You're welcome." Instead, say, "I know you would do the same for me."
Why? Here is Kawasaki: "Cialdini's phrase tells the person who received your favor that someday you may need help too, and it also signals to the person that you believe she is honorable and someone who will reciprocate. If this is the spirit in which you're saying it, your response is far more enchanting than the perfunctory 'You're welcome.' "