The sole cause of our weakness is the feebleness of our will, and we have always strength to perform what we strongly desire.
 Jean-Jacques Rousseau, Emile, or On Education (1762). copy citation

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Author Jean-Jacques Rousseau
Source Emile, or On Education
Topic weakness strength
Date 1762
Language English
Reference
Note Translated by Barbara Foxley
Weblink http://www.gutenberg.org/cache/epub/5427/pg5427-images.html

Context

“But let us suppose the maddest of men, the man who has his senses least under control; let him see the preparations for his death, let him realise that he will certainly die in torment a quarter of an hour later; not only would that man, from that time forward, become able to resist temptation, he would even find it easy to do so; the terrible picture with which they are associated will soon distract his attention from these temptations, and when they are continually put aside they will cease to recur. The sole cause of our weakness is the feebleness of our will, and we have always strength to perform what we strongly desire. "Volenti nihil difficile!" Oh! if only we hated vice as much as we love life, we should abstain as easily from a pleasant sin as from a deadly poison in a delicious dish.
How is it that you fail to perceive that if all the lessons given to a young man on this subject have no effect, it is because they are not adapted to his age, and that at every age reason must be presented in a shape which will win his affection?” source