Second, boredom typically occurs when people have trouble focusing their attention and they believe the reason for this difficulty is in the environment. When sitting in the airport, for example, there is probably a lot going on. There are people having conversations that you could listen to. You probably have something to read. There may be televisions showing the news. But, the stress of waiting for a delayed flight often makes it hard to concentrate, and so your mind jumps from one thing to another. You assume that this is caused by the environment, and so you feel boredom.

Lethargy is a state of tiredness, weariness, fatigue, or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to boredom, inadequate sleep, overexertion, overworking, stress, lack of exercise, or a symptom of a disorder. When part of a normal response, lethargy often resolves with rest, adequate sleep, decreased stress, and good nutrition.[21][22]
"If this is one of your tricks..." Like the time Torin had ordered hundreds of blow-up dolls and placed them throughout the fortress, all because Paris had foolishly complained about the lack of female companionship in town. The plastic "ladies" had stared our from every corner, their wide eyes and let-me-suck-you mouths taunting everyone who passed them.
“I asked myself whether a life devoid of any affection, of any goal, a life one fills with a thousand trifles intended to relieve its monotony, populated with human beings one seeks out in order not to be alone and whom one flees to avoid being bored by them, whether such a life isn't ridiculous, whether anything whatsoever wouldn't be preferable.”
Lethargy is a state of tiredness, weariness, fatigue, or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to boredom, inadequate sleep, overexertion, overworking, stress, lack of exercise, or a symptom of a disorder. When part of a normal response, lethargy often resolves with rest, adequate sleep, decreased stress, and good nutrition.[21][22]
^ Vodanovich, Stephen J. (November 2003) "Psychometric Measures of Boredom: A Review of the Literature" The Journal of Psychology. 137:6 p. 569 "Indeed, a shortcoming of the boredom literature is the absence of a coherent, universally accepted definition. The lack of an agreed-upon definition of boredom has limited the measurement of the construct and partly accounts for the existence of diverse approaches to assessing various subsets of boredom."
One more key element of boredom is control. Boredom often occurs when you have little control over your situation. Waiting rooms, lectures, and airline gates are all places where you have little control over your situation. Normally, we react to unpleasant situations by changing the situation. If you don’t like a book you are reading, for example, you close it and do something else. Boredom happens when you are unable to change the situation.  
Without stimulus or focus, the individual is confronted with nothingness, the meaninglessness of existence, and experiences existential anxiety. Heidegger states this idea as follows: "Profound boredom, drifting here and there in the abysses of our existence like a muffling fog, removes all things and men and oneself along with it into a remarkable indifference. This boredom reveals being as a whole."[27] Schopenhauer used the existence of boredom in an attempt to prove the vanity of human existence, stating, "...for if life, in the desire for which our essence and existence consists, possessed in itself a positive value and real content, there would be no such thing as boredom: mere existence would fulfil and satisfy us."[28]
When the antiproton was discovered … it sent a wave of ennui through the physics community. Not that its discovery was unimportant, but on the basis of Dirac's theory, everybody expected it. — Roger G. Newton, The Truth of Science, 1997 Chauncey and I were keen enough about our aesthetic solution to the ennui of war to try to proselytize others. He organized discussion groups with the crew; I took volunteers to visit landmarks … — Louis Auchincloss, "Atlantic War," in Authors at Sea, ed. Robert Shenk,  1997 The attendant outside was standing on tennis balls, exercising the soles of her feet, her body swaying back and forth with the ennui of jelly. — Edna O'Brien, New Yorker, 17 June 1991 Thus the days of life are consumed, one by one, without an object beyond the present moment; ever flying from the ennui of that, yet carrying it with us … — Thomas Jefferson, in a letter dated 7 Feb. 1787 Thomas Jefferson: Writings,  1984 the kind of ennui that comes from having too much time on one's hands and too little will to find something productive to do
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