This body is made of material nature, and we are within this body. Dehino 'smin yatha dehe kaumaram yauvanam jara [Bg. 2.13]. So long we have got this body, material body, we must be unhappy. First of all, we must try to understand why we are unhappy. We are unhappy because we are in this material body. What is that unhappiness? It is ending in four principles, janma-mrtyu-jara-vyadhi [Bg. 13.9]. To take birth and again to die, and so long we live we must suffer from some disease, and we must become old. Plain truth.
Lecture on Bhagavad-gita 4.10, Vrndavana, August 2, 1974