Kierkegaard said, "Boredom is the root of all evil."

"Existence" is a logical category in Hegel, but Kierkegaard defines it as a concept that applies to the individual. "Existence" refers to a person's own life process, including self-participation, free choice and self-realization. The Kirkegos natively defined an important theme in the philosophy of "existence."

Kierkegaard believed that there were three stages of life: the aesthetic stage, the moral stage, and the religious stage. He stressed that people may live in a lower stage and then suddenly jump to a higher stage, of course, many people live in the same stage throughout their lives. People who live in the aesthetic stage only live for the present, so they will seize every opportunity for pleasure. Such a person lives entirely in the world of the senses and is a slave to his or her own desires and emotions, including vanity. For them, anything that is annoying is bad. People who live in the aesthetic phase are prone to anxiety, fear, or emptiness. Kierkegaard said, "Boredom is the root of all evil." Man enjoys pleasure because of boredom, more bored because of pleasure, and eventually cruelty, self-harm and death. Whether or not to jump from the aesthetic stage to the moral or religious stage must be a decision from the heart of the individual. Living in the moral stage means having a serious attitude towards life, and consistently making moral choices, beginning to care about the right and wrong of things, while people living in the aesthetic stage only focus on whether it is interesting or not. There are also those who further ascend to the stage of religion, and they choose faith.

Kierkegaard points out that choices about oneself are also choices about subjective truths, about existence and belief. Choice is bound to be painful and accompanied by fear, a process that Kierkegaard calls a "leap," after which one enters the second stage, the moral stage, and even the third stage, the religious stage.

Soren Aabye Kierkegaard (1813–1855), also translated as "Kierkegaard", was a Danish psychologist and poet of religious philosophy, the founder of modern existential philosophy, the forerunner of postmodernism, and the forerunner of modern humanistic psychology.