Perfect sincerity, holiness, gigantic intellect, and all-conquering will. Let only a handful of men work with these, and the whole world will be revolutionized.
If you have done the best you can do and if you have gotten all you could extract from something, you have given all you had to give, then the time has come when you can do no more than say thank you and move on.
Constant development is the law of life, and a man who always tries to maintain his dogmas in order to appear consistent drives himself into a false position.