Nighttime Bourbon? ... The Virtue of Play
I answer that, Just as man needs bodily rest for the body's refreshment, because he cannot always be at work, since his power is finite and equal to a certain fixed amount of labor, so too is it with his soul, whose power is also finite and equal to a fixed amount of work. Consequently when he goes beyond his measure in a certain work, he is oppressed and becomes weary, and all the more since when the soul works, the body is at work likewise, in so far as the intellective soul employs forces that operate through bodily organs. Now sensible goods are connatural to man, and therefore, when the soul arises above sensibles, through being intent on the operations of reason, there results in consequence a certain weariness of soul, whether the operations with which it is occupied be those of the practical or of the speculative reason. Yet this weariness is greater if the soul be occupied with the work of contemplation, since thereby it is raised higher above sensible things; although perhaps certain outward works of the practical reason entail a greater bodily labor. On either case, however, one man is more soul-wearied than another, according as he is more intensely occupied with works of reason. Now just as weariness of the body is dispelled by resting the body, so weariness of the soul must needs be remedied by resting the soul: and the soul's rest is pleasure, as stated above (I-II:25:2; I-II:31:1 ad 2). Consequently, the remedy for weariness of soul must needs consist in the application of some pleasure, by slackening the tension of the reason's study. Thus in the Conferences of the Fathers xxiv, 21, it is related of Blessed John the Evangelist, that when some people were scandalized on finding him playing together with his disciples, he is said to have told one of them who carried a bow to shoot an arrow. And when the latter had done this several times, he asked him whether he could do it indefinitely, and the man answered that if he continued doing it, the bow would break. Whence the Blessed John drew the inference that in like manner man's mind would break if its tension were never relaxed.
Now such like words or deeds wherein nothing further is sought than the soul's delight, are called playful or humorous. Hence it is necessary at times to make use of them, in order to give rest, as it were, to the soul. This is in agreement with the statement of the Philosopher (Ethic. iv, 8) that "in the intercourse of this life there is a kind of rest that is associated with games": and consequently it is sometimes necessary to make use of such things.
I answer that, In human affairs whatever is against reason is a sin. Now it is against reason for a man to be burdensome to others, by offering no pleasure to others, and by hindering their enjoyment. Wherefore Seneca [Martin of Braga, Formula Vitae Honestae: cap. De Continentia] says (De Quat. Virt., cap. De Continentia): "Let your conduct be guided by wisdom so that no one will think you rude, or despise you as a cad." Now a man who is without mirth, not only is lacking in playful speech, but is also burdensome to others, since he is deaf to the moderate mirth of others. Consequently they are vicious, and are said to be boorish or rude, as the Philosopher states (Ethic. iv, 8).
Since, however, mirth is useful for the sake of the rest and pleasures it affords; and since, in human life, pleasure and rest are not in quest for their own sake, but for the sake of operation, as stated in Ethic. x, 6, it follows that "lack of mirth is less sinful than excess thereof." Hence the Philosopher says (Ethic. ix, 10): "We should make few friends for the sake of pleasure, since but little sweetness suffices to season life, just as little salt suffices for our meat."
https://www.newadvent.org/summa/3168.htm#article4
