“It is better to fail in originality, than to succeed in imitation. He who has never failed somewhere, that man can not be great. Failure is the true test of greatness. And if it be said, that continual success is a proof that a man wisely knows his powers, — it is only to be added, that, in that case, he knows them to be small. Let us believe it, then, once for all, that there is no hope for us in these smooth pleasing writers that know their powers.”

Frame of Government (1682)
Context: When the great and wise God had made the world, of all his creatures, it pleased him to chuse man his Deputy to rule it: and to fit him for so great a charge and trust, he did not only qualify him with skill and power, but with integrity to use them justly. This native goodness was equally his honour and his happiness; and whilst he stood here, all went well; there was no need of coercive or compulsive means; the precept of divine love and truth, in his bosom, was the guide and keeper of his innocency. But lust prevailing against duty, made a lamentable breach upon it; and the law, that before had no power over him, took place upon him, and his disobedient posterity, that such as would not live comformable to the holy law within, should fall under the reproof and correction of the just law without, in a judicial administration.

§ III
1910s, At the Feet of the Master (1911)

The Notebooks of Leonardo da Vinci (1883), XIX Philosophical Maxims. Morals. Polemics and Speculations.
Source: Leonardo's Notebooks

On Practice (1937)
Original: (zh-CN) 人们要想得到工作的胜利即得到预想的结果，一定要使自己的思想合于客观外界的规律性，如果不合，就会在实践中失败。人们经过失败之后，也就从失败取得教训，改正自己的思想使之适合于外界的规律性，人们就能变失败为胜利，所谓“失败者成功之母”，“吃一堑长一智”，就是这个道理。

Listen, Little Man! (1948)
Context: The Little Man does not know that he is little, and he is afraid of knowing it. He covers up his smallness and narrowness with illusions of strength and greatness, of others' strength and greatness. He is proud of his great generals but not proud of himself. He admires thought which he did not have and not the thought he did have. He believes in things all the more thoroughly the less he comprehends them, and does not believe in the correctness of those ideas which he comprehends most easily.

Memorial dedication (1902)

Nobel Prize Speech (1954)
Context: Things may not be immediately discernible in what a man writes, and in this sometimes he is fortunate; but eventually they are quite clear and by these and the degree of alchemy that he possesses he will endure or be forgotten. Writing, at its best, is a lonely life. Organizations for writers palliate the writer's loneliness but I doubt if they improve his writing. He grows in public stature as he sheds his loneliness and often his work deteriorates. For he does his work alone and if he is a good enough writer he must face eternity, or the lack of it, each day. For a true writer each book should be a new beginning where he tries again for something that is beyond attainment. He should always try for something that has never been done or that others have tried and failed. Then sometimes, with great luck, he will succeed.

Country Town Sayings (1911), p298.