Acharya Prashant explains that the root cause of fear in life is the fact that everything we consider our own has been acquired from the outside. He defines 'the other' as anything that is not the self, including people, situations, or time. Because our identity, reputation, and self-concept are derived from external sources, there is a constant underlying anxiety that these can be taken away by the same external forces. This dependency on others for self-validation creates a state of perpetual insecurity and fear.