Acharya Prashant explains that 'oldness' in a spiritual sense refers to anything that provides security to the ego or acts as a protective shield. It is not about objects or people, but a perspective that uses them for self-preservation. This tendency to remain safe is driven by fear and the foolishness of trying to protect an existence that is inherently indestructible. He describes the 'old stream of mind' as a state of constant, irrational anxiety where one cries out for protection without understanding the source of the danger. This attachment to security and temporary relief prevents true liberation, as people often prefer the comfort of their familiar fears over the transformative power of truth.