Only in the last decade has there been much scientific research looking into the nature of boredom. In 2006, a study classified boredom into four different types, with a follow-up study published this month in the journal Motivation and Emotion adding a fifth kind of boredom, called apathetic boredom, to the list. The researchers involved in the study had 63 university students and 80 high school students answer smartphone-based surveys about their activities and experiences over the course of two weeks.
This example leads to another key aspect of boredom. As Eastwood, Frischen, Fenske, and Smilek point out, bored people become aware of their difficulty concentrating. As a result, bored people often try to amuse themselves by daydreaming and letting their mind wander. Interestingly, while mind wandering helps people to keep their minds occupied, studies suggest that the more your mind wanders, the more bored you feel. The idea is that you recognize that this daydreaming is meant to occupy your mind, and so you realize that the situation is boring.
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.  
This kind of boredom is different from the others. Like reactant boredom, it’s also unpleasant, but a person experiencing it has low arousal and a lack of positive or negative feelings–in other words, a feeling of helplessness or depression. Of the high school students sampled in the study, 36% of boredom experiences were of the apathetic kind, which is worrisome given that other studies have shown that boredom, depression, and destructive behaviors are often linked.
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.

“Boredom is a flight from what is important. Like workaholism and perfectionism, it is a way of distracting yourself from inner experiences. It occurs when you look outward and do not find anything to engage your attention. Instead of feeling your emotions - becoming aware of the functioning of your energy system - you become bored. Boredom ... is a flight from your higher potential. It is fear of the transformation that wants to occur, and will occur in you, when you explore your emotions. It is your resistance to spiritual growth.”
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).