Sincerity is the virtue of speaking truly about one's 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".
Surprisingly, sincerity has not always been regarded a virtue in Western culture. It appears to have become an ideal for the first time in Europe and North America in the 17th century; and it gained considerable momentum during the Romantic movement, when sincerity was first celebrated as an artistic and social ideal. Indeed, in mid- to late-nineteenth century America, sincerity was an idea reflected in mannerisms, hairstyles, women's dress, and the literature of the time.
More recently, sincerity has been under assault by several modern developments such as psychoanalysis and postmodern developments such as deconstruction. Some scholars view sincerity as a construct rather than a moral virtue—although any virtue can be construed as a 'mere construct' rather than an actual phenomenon.
Literary critic Lionel Trilling dealt with the subject of sincerity, its roots, its evolution, its moral quotient, and its relationship to authenticity in a series of lectures published under the title Sincerity and Authenticity.

Etymology
An often repeated etymology proposes that "sincere" derived from the Latin sine = "without", cera = "wax". According to this explanation, dishonest sculptors in Rome or Greece would cover flaws in their work with wax to deceive the viewer, therefore, a sculpture "without wax" would mean honesty in its perfection.
There is some controversy over the source of the word. The Oxford English Dictionary states "There is no probability in the old explanation from sine cera 'without wax'". Instead, the OED explains "sincere" actually derives from the Latin sincerus meaning "clean, pure, sound". According to the American Heritage Dictionary[1], the Latin word "sincerus" is derived from the Indo-European root *sm̥kēros, itself derived from the zero-grade of *sem ("one") and the suffixed, lengthened e-grade of *ker ("grow"), generating the underlying meaning "of one growth", hence "pure, clean".