Meditation 5.16-17
16. As are your repeated imaginations so will your mind be, for the soul is dyed by its imaginations. Dye it, then, in a succession of imaginations like these: for instance, where it is possible to live, there also it is possible to live well: but it is possible to live in a palace, ergo it is also possible to live well in a palace. Or once more: a creature is made for that in whose interest it was created: and that for which it was made, to this it tends: and to what it tends, in this is its end: and where its end is, there is the advantage and the good alike of each creature: therefore fellowship is the good of a reasonable creature. For it has been proved long ago that we are born for fellowship; or was it not plain that the inferior creatures are in the interests of the superior, the superior of one another? But the animate are superior to the inanimate and the reasoning to the merely animate.
17. To pursue the impossible is madness: but it is impossible for evil men not to do things of this sort.