“The secret of success is sincerity. Once you can fake that, you've got it made.”
— Jean Giraudoux
Attributed to Giraudoux in Murphy's Law Book Two by Arthur Bloch (1980). Also associated with George Burns and Groucho Marx. The earliest print version dates to 1971.
I spent thirty years in the French diplomatic service. I sat across from ministers who smiled while lying, generals who shook hands while planning betrayals. The most dangerous people are not those who hide intentions, but those who make you believe they have none. Sincerity is a performance. Be honest about what you are faking. That is the only sincerity worth having.