If there was nothing wrong in the world there wouldn't be anything for us to do.
No man who is occupied in doing a very difficult thing, and doing it very well, ever loses his self-respect.
Success does not consist in never making mistakes but in never making the same one a second time.
A life spent making mistakes is not only more honourable, but more useful than a life spent doing nothing.
The moment we want to believe something, we suddenly see all the arguments for it, and become blind to the arguments against it.