Nienna said:
And, yet, Gurdjieff has also written that, "Sincerity with everyone is a weakness."
Absolutely. One example of that from pop culture is Michael Scott from The Office. He is pathologically incapable of being insincere with ANYONE, except himself. What is REQUIRED is sincerity with the SELF, on the path of self perfection. It is amazing how easy it is to slip into insincerity while still thinking you are being sincere.
Kris