Question: Did Aquinas or Aristotle discuss what happens to the man when he feels bored? What do they say about it? How do they explain that feeling? I coupled Aristotle and Aquinas in this question because Aquinas is famous commentator on him and developed his thought.
There could be difficulty in finding precise comments by both Aristotle and Thomas Aquinas on 'boredom', as generally conceived as "being weary due to being unoccupied or lacking interest in one's current activity." However, this does not mean that we cannot infer what their thoughts could have been concerning boredom from what it is that they have explicitly stated.
St. Thomas Aquinas from the "The Summa Theologica", Second Part of the Second Part, Question: 35, titled, 'Of Sloth' states the following concerning what is called 'sloth':
I answer that, sloth [acedia], according to Damascene (De Fide Orth. ii, 14) is an oppressive sorrow, which, to wit, so weighs upon man's mind, that he wants to do nothing; thus acid things are also cold. Hence sloth implies a certain weariness of work, as appears from a gloss on Ps.106:18, "Their soul abhorred all manner of meat," and from the definition of some who say that sloth is a "sluggishness of the mind which neglects to begin good.
The term 'acedia', translated as 'sloth' in the English, in the Latin derives from the Greek term 'ἀκηδία' which, according to Wiktionary, roughly means "carelessness or lack of care." There are no translations of "The Summa Theologica", to which I could immediately recall to memory, that render the Latin term 'acedia' to boredom since: If Aquinas were to have been speaking about 'boredom' he might have instead used the phrase 'taedium vitae'. Despite this, reading the Latin term, one could * possibly * translate the term to read boredom without extrapolating from Aquinas either.
The conclusion which Thomas Aquinas arrives reads as follows:
Accordingly, since sloth [acedia], as we understand it here, denotes sorrow for spiritual good, it is evil on two counts, both in itself and in point of its effect. Consequently, it is a sin, for by sin we mean an evil movement of the appetite, as appears from what has been said above.
There's much to take from Aristotle due to his notable work "The Nicomachean Ethics", however, there is not much, if anything, explicitly pertaining to boredom as such. Nevertheless, there are passages that might allow us to conjecture what his thoughts might have been concerning boredom.
Aristotle from "The Nicomachean Ethics", Chapter 9-10, Sec: 1100a - 1101a, extols the goods which derive from happiness. He states in one passage the following:
What is to prevent us, then, from concluding that the happy person is the one who, adequately furnished with external goods, engages in activities in accordance with complete virtue, not for just any period of time but over a complete life?
There is an emphasis throughout the ninth and eleventh chapters of "The Nicomachean Ethics" for individuals to undergo activities that purse virtue. The relevant chapters on "The Nicomachean Ethics" can be found in the reference below [ 4 ].
And one last interesting note, Robert C. Solomon in his book, titled, "In Defense of Sentimentality", states the following:
. . . . in Aristotle's terms, we might look at sloth as a vice of deficiency, whether of physical energy or of aspiration.
Hopefully this response was of some service to you, cheers!
[ 1 ]: "The Summa Theologica", Second Part of the Second Part, Question: 35
[ 2 ]: Wiktionary Entries on 'acedia'
[ 3 ]: Some Ancient Notions of Boredom by Peter Toohey
[ 4 ]: A Sample of "The Nicomachean Ethics" by Aristotle