Afear of something that is not a hazard is a

Phobia

Explanation:

if it's seen by people with normal psychological condition, source of phobia often easily overlooked since it does not possess the ability to hurt or injures us. But, to a people with phobia, that seemingly harmless object will cause unreasonable and excessive fear in their mind.

Phobia is most likely caused by a psychological trauma that we experienced in the past. The object that remind us with that trauma will be most likely become the trigger that is causing the phobia.

For example,

Children who are often being caged in a small room as a form of 'punishment' by their parents has a higher chance to grow up to be claustrophobic (having irrational fear if they are in confined space,  like an elevator in their office)

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