The memory of the past unfulfilled desires traps energy, which manifests itself as a person. When its charge gets exhausted, the person dies.
Unfulfilled desires are carried over into the birth.
Self-identification with body creates ever-fresh desires and there is no end to them unless this mechanism of bondage is clearly seen. It is clarity that is liberating, for you cannot abandon desire unless its causes and effects are clearly seen.
I do not say that the same person is reborn. It dies, and dies for good. But its memories remain and their desires and fears. They supply the energy for a new person.
— Sri Nisargadattta Maharaj