The Oxford English Dictionary and most scholars state that sincerity from sincere is derived from the Latin sincerus meaning clean, pure, sound (1525–35). Sincerus may have once meant "one growth" (not mixed), from sin- (one) and crescere (to grow). Sincerity is the virtue of one who speaks truly about his or her own feelings, thoughts, desires. Sincere expression carries risks to the speaker, since the ordinary screens used in everyday life are opened to the outside world. At the same time, we expect our friends, our lovers, our leaders "to be sincere". 

Followers of Brandy Buckhalter