It could be as simple as this: My son was a terrible pianist. He completely lacked talent. After his recitals at age 10, I would pretend to be enthralled. He knew he was awful and he knew I knew he was awful, but it was appropriate that I not admit what I knew. It is called politeness and sometimes affection. There is rarely affection among nations, but politeness calls for behaving differently when a person is in the company of certain other people than when that person is with colleagues talking about those people. This is the simplest of human rules. Not admitting what you know about others is the foundation of civilization. The same is true among diplomats.
George Friedman. Via