What fundamental error, according to this scripture, traps a soul in the endless cycle of birth and death (Samsara)?

As explained in Chapter 37, the perpetual cycle of worldly existence, known as Samsara, is driven by a deluded perception of duality. The fundamental error occurs when a soul, clouded by ignorance, holds the belief that "Parabrahman is different from me; I am not that, I am something else." This knowledge of difference, this feeling of separation from the ultimate reality, is what subjects an individual to the eternal wheel of existence where death follows birth, and rebirth inevitably follows death.