The success of diplomacy lies in truly understanding the needs and interests of the other party, and seeking possibilities for cooperation based on that understanding.
Diplomats should have the ability to respect and understand other countries and cultures, as well as the ability to communicate across language and cultural barriers.
The ideas of economists and political philosophers, both when they are right and when they are wrong, are more powerful than is commonly understood. Indeed the world is ruled by little else. Practical men, who believe themselves to be quite exempt from any intellectual influence, are usually the slaves of some defunct economist.