It is perfectly monstrous,' he said, at last, 'the way people go about nowadays saying things against one behind one's back that are absolutely and entirely true.
Something might be true while being harmful and dangerous in the highest degree. Indeed, it might be a basic characteristic of existence that those who know it completely would perish, in which case the strength of a spirit should be measured according to how much of the 'truth' one could still barely endure- or to put it more clearly, to what degree one would require it to be thinned down, shrouded, sweetened, blunted, falsified.
Perhaps there is no other knowing than the mere competence of the act. If at the heart of one's being, there is no self to which one ought to be true, then sincerity is simply nerve; it lies in the unabashed vigor of the pretense. But pretense is only pretense when it is assumed that the act is not true to the agent. Find the agent.