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.
Talent for talent's sake is a bauble and a show. Talent working with joy in the cause of universal truth lifts the possessor to new power as a benefactor.
I believe it is an established maxim in morals that he who makes an assertion without knowing whether it is true or false, is guilty of falsehood; and the accidental truth of the assertion, does not justify or excuse him.
Your bait of falsehood takes this carp of truth,
And thus do we of wisdom and of reach,
With windlasses and with assays of bias,
By indirections find directions out.
So with truth - there is a certain moment when one can say, this is the truth and here I put a dot, a stop, and I go to another thing. A judge has to put an end to a deliberation. But for a historian, theres never an end to the past. It can go on and on and on.
Chaos of thought and passion, all confused; Still by himself abused or disabused; Created half to rise, and half to fall; Great lord of all things, yet a prey to all; Sole judge of truth, in endless error hurled,- The glory, jest, and riddle of the world.