La Rochefoucauld, expressing a commonplace with the penetrative terseness that made him a master of the apophthegm, pronounced it “not to be enough to have great qualities:  a man must have the economy of them.”  Or, as another writer says:  “Empire in this world belongs not so much to wits, to talents, and to industry, as to a certain skilful economy and to the continual management that a man has the art of applying to all his other gifts."[18] Notwithstanding the peril that haunts superlative propositions, we are inclined to say that Diderot is the most striking illustration of this that the history of letters or speculation has to furnish.  If there are many who have missed the mark which they or kindly intimates thought them certain of attaining, this is mostly not for want of economy, but for want of the great qualities which were imputed to them by mistake.  To be mediocre, to be sterile, to be futile, are the three fatal endings of many superbly announced potentialities.  Such an end nearly always comes of exaggerated faculty, rather than of bad administration of natural gifts.  In Diderot were splendid talents.  It was the art of prudent stewardship that lay beyond his reach.  Hence this singular fact, that he perhaps alone in literature has left a name of almost the first eminence, and impressed his greatness upon men of the strongest and most different intelligence, and yet never produced a masterpiece; many a fine page, as Marmontel said, but no one fine work.

No man that ever wrote was more wholly free from that unquiet self-consciousness which too often makes literary genius pitiful or odious in the flesh.  He put on no airs of pretended resignation to inferior production, with bursting hints of the vast superiorities that unfriendly circumstance locked up within him.  Yet on one occasion, and only on one, so far as evidence remains, he indulged a natural regret.  “And so,” he wrote when revising the last sheets of the Encyclopaedia (July 25, 1765), “in eight or ten days I shall see the end of an undertaking that has occupied me for twenty years; that has not made my fortune by a long way; that has exposed me many a time to the risk of having to quit my country or lose my freedom; and that has consumed a life that I might have made both more useful and more glorious.  The sacrifice of talent to need would be less common, if it were only a question of self.  One could easily resolve rather to drink water and eat dry crusts and follow the bidding of one’s genius in a garret.  But for a woman and for children, what can one not resolve?  If I sought to make myself of some account in their eyes, I would not say—­I have worked thirty years for you:  I would say—­I have for you renounced for thirty years the vocation of my nature; I have preferred to renounce my tastes in doing what was useful for you, instead of what was agreeable to myself.  That is your real obligation to me, and of that you never think."[19]