Fear

 Scientifically ....
Fear is an emotion induced by a threat perceived by living entities, which causes a change in brain and organ function and ultimately a change in behavior, such as running away, hiding or freezing from traumatic events. Fear may occur in response to a specific stimulus happening in the present, or to a future situation, which is perceived as risk to health or life, status, power, security, or, in the case of humans, wealth or anything held valuable. The fear response arises from the perception of danger leading to confrontation with or escape from/avoiding the threat (also known as the fight-or-flight response), which in extreme cases of fear (horror and terror) can be a freeze response or paralysis.Scientifically ....

But to make clear in others we only fear the unknown or whatever can harm us physically or mentally ... fear is a emotion we can get rid and the key is to gain knowledge .
Knowledge about everything .... the smarter ones always overcomes their nightmares..