Different scholars use different definitions of boredom, which complicates research.[9] Boredom has been defined by Cynthia D. Fisher in terms of its main central psychological processes: "an unpleasant, transient affective state in which the individual feels a pervasive lack of interest and difficulty concentrating on the current activity."[10] Mark Leary et al. describe boredom as "an affective experience associated with cognitive attentional processes."[11] In positive psychology, boredom is described as a response to a moderate challenge for which the subject has more than enough skill.[12][full citation needed]
“Boredom – the psychological state that we experience whenever we are uninterested in what we are currently doing – is one of the defining traits of humanity. Time is the psychological nemesis of humankind. Tedium, a fundamental angst of humankind, arises from human beings’ ability to perceive time and our attempts to derive meaning from our personal existence.”
In Experience Without Qualities: Boredom and Modernity, Elizabeth Goodstein traces the modern discourse on boredom through literary, philosophical, and sociological texts to find that as "a discursively articulated phenomenon...boredom is at once objective and subjective, emotion and intellectualization—not just a response to the modern world but also a historically constituted strategy for coping with its discontents."[3] In both conceptions, boredom has to do fundamentally with an experience of time and problems of meaning.
Although it has not been widely studied, research on boredom suggests that boredom is a major factor impacting diverse areas of a person's life. People ranked low on a boredom-proneness scale were found to have better performance in a wide variety of aspects of their lives, including career, education, and autonomy.[30] Boredom can be a symptom of clinical depression. Boredom can be a form of learned helplessness, a phenomenon closely related to depression. Some philosophies of parenting propose that if children are raised in an environment devoid of stimuli, and are not allowed or encouraged to interact with their environment, they will fail to develop the mental capacities to do so.
^ 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."

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]

The bored antihero became prominent in early 20th century existentialist works such as Franz Kafka's The Metamorphosis (1915),[43] Jean-Paul Sartre's La Nausée (1938) (French for 'Nausea'),[44] and Albert Camus' L'Étranger (1942) (French for 'The Stranger').[45] The protagonist in these works is an indecisive central character who drifts through his life and is marked by ennui, angst, and alienation.[46]
There was also a piano, well littered with music, a sewing bag thrown down upon a cretonned window seat, and the generous fireplace was flanked by two huge baskets, one heaped with magazines, the other a perfectly round mound of yellow fur, which suddenly took form and life as a yellow tabby cat fastened hopeful topaz eyes upon them, blinked away a brief disappointment, and then yawned with ennui.