The Cream of the Jest by James Branch Cabell

Through such airdrawn surmises, then, as I have just recorded did Felix Kennaston enter at last into that belief which is man's noblest heritage.

"Or I would put it, rather, that belief is man's métier," Kennaston once corrected me -- "for the sufficient reason that man has nothing to do with certainties. He cannot ever get in direct touch with reality. Such is the immutable law, the true cream of the jest. Felix Kennaston, so long as he wears the fleshly body of Felix Kennaston, is conscious only of various tiny disturbances in his brain-cells, which entertain and interest him, but cannot pretend to probe to the roots of reality about anything. By the nature of my mental organs, it is the sensation the thing arouses in my brain of which I am aware, and never of the thing itself. I am conscious only of appearances. They may all be illusory. I cannot ever tell. But it is my human privilege to believe whatever I may elect."