Acharya Prashant explains that fear is essentially a thought rather than an action. He observes that while people are comfortable speaking in a vacant room or in front of a mirror, they experience fear when others are present. This indicates that fear is rooted in the thought of others and the potential judgment they might pass. He emphasizes that in the thick of action, fear disappears; it only exists as a mental anticipation before the action begins. This fear arises because individuals have borrowed their sense of identity, respect, and acceptance from society, and they are terrified that these external validations can be taken away by the same people who provided them.