Objection 1. It would seem that man does not will all, whatsoever he wills, for the last end. For things ordained to the last end are said to be serious matter, as being useful. But jests are foreign to serious matter. Therefore what man does in jest, he ordains not to the last end.
Objection 2. Further, the Philosopher says at the beginning of his Metaphysics [1, 2] that speculative science is sought for its own sake. Now it cannot be said that each speculative science is the last end. Therefore man does not desire all, whatsoever he desires, for the last end.
Objection 3. Further, whosoever ordains something to an end, thinks of that end. But man does not always think of the last end in all that he desires or does. Therefore man neither desires nor does all for the last end.
On the contrary, Augustine says (De Civ. Dei xix, 1): "That is the end of our good, for the sake of which we love other things, whereas we love it for its own sake."
I answer that, Man must, of necessity, desire all, whatsoever he desires, for the last end. This is evident for two reasons. First, because whatever man desires, he desires it under the aspect of good. And if he desire it, not as his perfect good, which is the last end, he must, of necessity, desire it as tending to the perfect good, because the beginning of anything is always ordained to its completion; as is clearly the case in effects both of nature and of art. Wherefore every beginning of perfection is ordained to complete perfection which is achieved through the last end. Secondly, because the last end stands in the same relation in moving the appetite, as the first mover in other movements. Now it is clear that secondary moving causes do not move save inasmuch as they are moved by the first mover. Therefore secondary objects of the appetite do not move the appetite, except as ordained to the first object of the appetite, which is the last end.
Reply to Objection 1. Actions done jestingly are not directed to any external end; but merely to the good of the jester, in so far as they afford him pleasure or relaxation. But man's consummate good is his last end.
Reply to Objection 2. The same applies to speculative science; which is desired as the scientist's good, included in complete and perfect good, which is the ultimate end.
Reply to Objection 3. One need not always be thinking of the last end, whenever one desires or does something: but the virtue of the first intention, which was in respect of the last end, remains in every desire directed to any object whatever, even though one's thoughts be not actually directed to the last end. Thus while walking along the road one needs not to be thinking of the end at every step.
Source: Summa Theologica (New Advent)