Fanaticism (from the Latin adverb fānāticē [fren-fānāticus; enthusiastic, ecstatic; raging, fanatical, furious]) is a belief or behavior involving uncritical zeal or an obsessive enthusiasm.
Philosopher George Santayana defines fanaticism as "redoubling your effort when you have forgotten your aim". The fanatic displays very strict standards and little tolerance for contrary ideas or opinions. Tõnu Lehtsaar has defined the term fanaticism as the pursuit or defence of something in an extreme and passionate way that goes beyond normality. Religious fanaticism is defined by blind faith, the persecution of dissidents and the absence of reality.
Fanaticism is a result from multiple cultures interacting with one another. Fanaticism occurs most frequently when a leader makes minor variations on already existing beliefs, which then drives the followers into a frenzy. In this case, fanaticism is used as an adjective describing the nature of certain behaviors that people recognize as cult-like. Mead referred to the style of defense used when the followers are approached. The most consistent thing presented is the priming, or preexisting, conditions and mind state needed to induce fanatical behavior. Each behavior is obvious once it is pointed out; a closed mind, no interest in debating the subject of worship, and over reaction to people who do not believe.
In his book Crazy Talk, Stupid Talk, Neil Postman states that "the key to all fanatical beliefs is that they are self-confirming....(some beliefs are) fanatical not because they are 'false', but because they are expressed in such a way that they can never be shown to be false."
The behavior of a fan with overwhelming enthusiasm for a given subject is differentiated from the behavior of a fanatic by the fanatic's violation of prevailing social norms. Though the fan's behavior may be judged as odd or eccentric, it does not violate such norms. A fanatic differs from a crank, in that a crank is defined as a person who holds a position or opinion which is so far from the norm as to appear ludicrous and/or probably wrong, such as a belief in a Flat Earth. In contrast, the subject of the fanatic's obsession may be "normal", such as an interest in religion or politics, except that the scale of the person's involvement, devotion, or obsession with the activity or cause is abnormal or disproportionate to the average.[ambiguous]