"If we consider all external goods as equally beyond our power, we shall no more regret the absence of such goods... when deprived of them without any fault of ours, than our not possessing the kingdoms of China or Mexico; and thus making... a virtue of necessity, we shall no more desire health in disease, or freedom in imprisonment, than we now do bodies incorruptible as diamonds, or the wings of birds to fly with. But I confess there is need of prolonged discipline and frequently repeated meditation to accustom the mind to view all objects in this light; and I believe that in this chiefly consisted the secret of the power of such philosophers as in former times were enabled to rise superior to the influence of fortune, and, amid suffering and poverty, enjoy a happiness which their gods might have envied. For, occupied incessantly with the consideration of the limits prescribed to their power by nature, they became so entirely convinced that nothing was at their disposal except their own thoughts, that this conviction was of itself sufficient to prevent their entertaining any desire of other objects; and over their thoughts they acquired a sway so absolute, that they had some ground on this account for esteeming themselves more rich and more powerful, more free and more happy, than other men who, whatever be the favors heaped on them by nature and fortune, if destitute of this philosophy, can never command the realization of all their desires."
Discourse on the Method of Rightly Conducting One's Reason and of Seeking Truth in the Sciences is a philosophical and autobiographical treatise published by René Descartes in 1637. It is best known as the source of the famous quotation "Je pense, donc je suis", which occurs in Part IV of the work. A similar argument without this precise wording is found in Meditations on First Philosophy (1641),
"The greatest minds, as they are capable of the highest excellencies, are open likewise to the greatest aberrations; and those who travel very slowly may yet make far greater progress, provided they keep always to the straight road, than those who, while they run, forsake it."
"Each problem that I solved became a rule, which served afterwards to solve other problems."
"The last rule was to make enumerations so complete, and reviews so comprehensive, that I should be certain of omitting nothing."
"The first precept was never to accept a thing as true until I knew it as such without a single doubt."
"Divide each difficulty into as many parts as is feasible and necessary to resolve it."
"Car ce nest pas assez davoir lesprit bon, mais le principal est de lappliquer bien."