"For it is not enough to have a good mind; the main thing is to apply it well. The greatest souls are capable of the greatest vices as well as the greatest virtues; and those who proceed but very slowly can make much greater progress, if they always follow the right path, than those who hurry and stray from it." 
- Rene Descartes, Part I of 'Discourse on the Method'


"For with our declining standards of behaviour, few people are willing to say everything that they believe; and besides, many people do not know what they believe, since believing something and knowing that one believes it are different acts of thinking, and the one often occurs without the other.  "
-Rene Descartes, Part III of 'Discourse on the Method'