Concupiscentia est causa doloris quia omne quod impedit motum ne perveniat ad terminum, est contrarium motui.
Desire is a cause of pain because whatever hinders a movement from reaching its end is contrary to that movement.
Illud autem quod est contrarium motui appetitus, est contristans. Et sic per consequens concupiscentia fit causa tristitiae, inquantum de retardatione boni concupiti, vel totali ablatione, tristamur.
Now that which is contrary to the movement of the appetite, is a cause of sadness. Consequently, desire becomes a cause of sadness, insofar as we are sad for the delay of a desired good, or for its entire removal.
Universalis autem causa doloris esse non potest, quia magis dolemus de subtractione bonorum praesentium, in quibus iam delectamur, quam futurorum, quae concupiscimus.
But it cannot be a universal cause of pain, because we are pained more for the loss of present good, in which we have already taken pleasure, than for the withdrawal of future good which we desire to have.
Concupiscentia est delectabilis, quandiu manet spes adipiscendi quod concupiscitur. Sed, subtracta spe per impedimentum appositum, concupiscentia dolorem causat.
Desire gives pleasure, so long as there is hope of obtaining that which is desired. But, when hope is removed through the presence of an obstacle, desire causes pain.
Augustinus dicit, in Enchirid., "subintrantibus ignorantia agendarum rerum, et concupiscentia noxiarum, comites subinferuntur error et dolor".
Augustine says (Enchiridion xxiv): "When ignorance of things necessary to be done, and desire of things hurtful, found their way in, then error and pain stole an entrance in their company."