Korean professor explains background of the mentality.

Pseudologia fantastica, mythomania, or pathological lying, is one of several terms applied by psychiatrists to the behaviour of habitual or compulsive lying.
It was first described in the medical literature in 1891. One definition of pathological lying is the following: "Pathological lying is falsification entirely disproportionate to any discernible end in view, may be extensive and very complicated, and may manifest over a period of years or even a lifetime."[1]

The defining characteristics of pseudologia fantastica are that, first, the stories are not entirely improbable and often have some element of truth. They aren't a manifestation of delusion or some wider form of psychosis: upon confrontation, the person can acknowledge them to be untrue, even if unwillingly. Second, the fabricative tendency is long lasting; it is not provoked by the immediate situation or social pressure as much as it originates with the person's innate urge to act in accordance. Third, a definitely internal, not an external, motive for the behavior can be clinically discerned. E.g. long lasting extortion or habitual spousal battery might cause a person to lie repeatedly, without the lying being a pathological symptom. Fourth, the stories told tend towards presenting the person in question in a good light. For example, the person might be presented as being fantastically brave, knowing or being related to many famous people.

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Part2

Ancient Korean Empire Hwanguk by uriginalworld

Chosonninja doesn't know what Nintai really means.
He selected the word Nintiajutsu just because it sounded similar to Ninjutsu.