Tatamasy, Ah, and Thou Art, Tat Amasy?

Sage Uddalaka asks his son Svetaketu: What is that knowledge by which we hear the unhearable, perceive what cannot be perceived and know what cannot be known? Inspired from this story from the Chandogya Upanishad, Swami Sarvapriyananda teaches the great saying (mahavakya) - Tat Tvam Asi (That Thou Art). This discourse is also inspired from a verse from the Brihadharanyaka Upanishad (Mantra 4.4.12) as taught in the book, Pancadasi by Vidyaranya: "If a man knows the Self as ‘I am this,’ then desiring what and for whose sake will he suffer in the wake of the body?" Mantra 4.4.12: आत्मानं चेद्विजानीयादयमस्मीति पूरुषः । किमिच्छन्कस्य कामाय शरीरमनुसंज्वरेत् ॥ १२