It is dangerous to be sincere unless you are also stupid. George Bernard Shaw
A friend is a person with whom I may be sincere. Before him, I may think aloud. Ralph Waldo Emerson
Sincerity is the key which will open the door through which you will see your separate parts, and you will see something quite new. You must go on trying to be sincere. Each day you put on a mask, and you must take it off little by little. G. I. Gurdjieff
My definition of an educated man is the fellow who knows the right thing to do at the time it has to be done. You can be sincere and still be stupid. Charles Kettering
I will add that I do not believe his admiration of my person, dazzling through I am, to be sincere. He told me I was a beautiful, sparkling lady. Cassandra Clare
All that is necessary to paint well is to be sincere. Maurice Denis