According to Wikipedia, fear is an emotional response to a perceived threat.  Fear has the potential to be a significant motivator of human action, in-action, and specific behaviors.

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"Take him to the dungeon!"

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In past ages, direct fear imposed by powerful rulers was used to control the masses, control the individual and motivate society to enact the will of the ruler.  The world has never been without such methods being employed.  Basically, the transaction includes a club in the hand of the powerful with the threat of the use of the club as the motivation for the ‘governed’ to comply with the wishes of the ruler.  The prudent tyrannical ruler endeavors to minimize the use of the club. His primary aim is not to harm, but instead to control.  We are all familiar with these processes of the bully, but in the modern era, most of Western civilization dispensed with allowing these methods to be the normal order of society.

In the 17^th Century, some among The People, got their act together and developed a concept known as the Social Contract.  This was the introduction into an understanding across society that the authority of the state was derived from the “consent of the governed.”  Thus developed an antithesis of tyranny.

However, there is some feature within human nature that drives some to desire to attempt to be the masters over all the rest.  Observation demonstrates a driving force behind this that is beyond the simple explanation of ambition, self-preservation, or just trying to get ahead. These are factors, but there is one factor that is deeper; there is an element of evil that motivates men to strive to be master over all others.  Therefore, there is always a certain pressure for humanity to be approaching tyranny, a vector that is resisted only by the will of individuals willing to defend the liberty of themselves and of others.

» More: The Fear Formula