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.
Over immense periods of time the intellect produced nothing but errors. A few of these proved to be useful and helped to preserve the species: those who hit upon or inherited these had better luck in their struggle for themselves and their progeny. Such erroneous articles of faith... include the following: that there are things, substances, bodies; that a thing is what it appears to be; that our will is free; that what is good for me is also good in itself.
There is nothing more necessary than truth, and in comparison with it everything else has only secondary value. This absolute will to truth: what is it? Is it the will to not allow ourselves to be deceived? Is it the will not to deceive? One does not want to be deceived, under the supposition that it is injurious, dangerous, or fatal to be deceived.
...most men have bound their eyes with one or another handkerchief, and attached themselves to some one of these communities of opinion. This conformity makes them not false in a few particulars, authors of a few lies, but false in all particulars. Their every truth is not quite true. Their two is not the real two, their four not the real four; so that every word they say chagrins us, and we know not where to begin to set them right.
There are many hypotheses in science which are wrong. That’s perfectly all right: it’s the aperture to finding out what’s right. Science is a self-correcting process.