Boredom is similar to mental fatigue and is caused by repetition and lack of interest in the details of our tasks (such as tasks that require continuous attention, waiting at the airport, prisoners locked in cells). Any experience that is predictable and repetitive becomes boring. In general, too much of the same thing and too little stimulation can cause in its victim an absence of desire and a feeling of entrapment (Toohey, 2012).    

“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.”
Boredom also has its benefits. It is important to see boredom as a “call to action” (Svendsen, 1999). Nietzsche suggested that men of rare sensibility value boredom as an impetus to achievement. Boredom can be a catalyst for action. It can provide an opportunity for thought and reflection. It can also be a sign that a task is a waste of time—and thus not worth continuing.
Then, after a baseline EEG test measuring normal brain activity, the researchers assigned the participants a tedious task: they had to turn eight virtual pegs on a screen as the computer highlighted them. This activity lasted approximately 10 minutes, during which time the researchers used EEG caps to measure participants’ brain activity as they carried out the boring task.

The authors of this paper point to an interesting study by Robin Damrad-Frye and James Laird in the August 1989 issue of the Journal of Personality and Social Psychology. In this study, participants had to listen to a tape of a person reading a Psychology Today article. In the next room, there was a television soundtrack from a soap opera playing. For some groups listening to the article, the TV was very loud and distracting, for others it was barely noticeable, and for some it was not playing at all. After listening to the article, people rated their boredom during the study. 
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.
People who lack self-awareness are more prone to boredom. A bored individual is unable to articulate what it is that he or she desires or wants to do. They have trouble describing their feelings. An inability to know what will make one happy can lead to a more profound existential boredom. Not knowing what we are searching for means that we lack the capacity to choose appropriate goals for engagement with the world (Eastwood, 2012).
“To me, at least in retrospect, the really interesting question is why dullness proves to be such a powerful impediment to attention. Why we recoil from the dull. Maybe it’s because dullness is intrinsically painful; maybe that’s where phrases like ‘deadly dull’ or ‘excruciatingly dull’ come from. But there might be more to it. Maybe dullness is associated with psychic pain because something that’s dull or opaque fails to provide enough stimulation to distract people from some other, deeper type of pain that is always there, if only in an ambient, low-level way, and which most of us spend nearly all our time and energy trying to distract ourselves from feeling, or at least from feeling directly or with our full attention. Admittedly, the whole thing’s pretty confusing, and hard to talk about abstractly…but surely something must lie behind not just Muzak in dull or tedious places any more but now also actual TV in waiting rooms, supermarkets’ checkouts, airport gates, SUVs’ backseats. Walkman, iPods, BlackBerries, cell phones that attach to your head. This terror of silence with nothing diverting to do. I can’t think anyone really believes that today’s so-called ‘information society’ is just about information. Everyone knows it’s about something else, way down.”

In conventional usage, boredom is an emotional and occasionally psychological state experienced when an individual is left without anything in particular to do, is not interested in their surroundings, or feels that a day or period is dull or tedious. It is also understood by scholars as a modern phenomenon which has a cultural dimension. "There is no universally accepted definition of boredom. But whatever it is, researchers argue, it is not simply another name for depression or apathy. It seems to be a specific mental state that people find unpleasant—a lack of stimulation that leaves them craving relief, with a host of behavioural, medical and social consequences."[1] According to BBC News, boredom "...can be a dangerous and disruptive state of mind that damages your health"; yet research "...suggest[s] that without boredom we couldn't achieve our creative feats."[2]
There are three types of boredom, all of which involve problems of engagement of attention. These include times when we are prevented from engaging in wanted activity, when we are forced to engage in unwanted activity, or when we are simply unable for some other reason to maintain engagement in an activity.[13] Boredom proneness is a tendency to experience boredom of all types. This is typically assessed by the Boredom Proneness Scale.[14] Recent research has found that boredom proneness is clearly and consistently associated with failures of attention.[15] Boredom and its proneness are both theoretically and empirically linked to depression and similar symptoms.[16][17][18] Nonetheless, boredom proneness has been found to be as strongly correlated with attentional lapses as with depression.[16] Although boredom is often viewed as a trivial and mild irritant, proneness to boredom has been linked to a very diverse range of possible psychological, physical, educational, and social problems.[19]

“Alcohol makes other people less tedious, and food less bland, and can help provide what the Greeks called entheos, or the slight buzz of inspiration when reading or writing. The only worthwhile miracle in the New Testament—the transmutation of water into wine during the wedding at Cana—is a tribute to the persistence of Hellenism in an otherwise austere Judaea. The same applies to the seder at Passover, which is obviously modeled on the Platonic symposium: questions are asked (especially of the young) while wine is circulated. No better form of sodality has ever been devised: at Oxford one was positively expected to take wine during tutorials. The tongue must be untied. It's not a coincidence that Omar Khayyam, rebuking and ridiculing the stone-faced Iranian mullahs of his time, pointed to the value of the grape as a mockery of their joyless and sterile regime. Visiting today's Iran, I was delighted to find that citizens made a point of defying the clerical ban on booze, keeping it in their homes for visitors even if they didn't particularly take to it themselves, and bootlegging it with great brio and ingenuity. These small revolutions affirm the human.”
“Time is quixotic because it can torment us. When we have insufficient stimulus to fill our lives, we resent the relentless quality of time, and we engage in activities designed to “kill time.” Time that passes slowly creates insufferable boredom; time that passes to quickly makes us aware of our accelerated death march. A person’s perspective on time depends mostly on what they are most afraid of, boredom or death.”
The French loanword ennui comes from the very same Late Latin word that gave us annoy — inodiare ("to make loathsome"). We borrowed ennui several centuries after absorbing annoy into the language. Ennui deals more with boredom than irritation - and a somewhat specific sort of boredom at that. It generally refers to the feeling of jadedness that can result from living a life of too much ease. The poet Charles Lloyd described it well in his 1823 Stanzas to Ennui when he referred to that world-weary sensation as a "soul-destroying fiend" which visits with its "pale unrest / The chambers of the human breast / Where too much happiness hath fixed its home."