Prabhupada's lecture - Śrīmad-Bhāgavatam 1.15.1 - New York, November 29, 1973
So evaṁ kṛṣṇa sakhaḥ kṛṣṇo. Arjuna's name is Kṛṣṇa Sakha, and he is also called sometimes Kṛṣṇa, because Arjuna's bodily feature was almost similar to Kṛṣṇa's bodily feature. So, he was morose, being separated from Kṛṣṇa, and his elder brother was suggesting whether he was morose for this reason or that reason or this reason. Actually, he was unhappy on account of being separated from Kṛṣṇa. Similarly, not only Arjuna, all of us, we are also, as Kṛṣṇa, Arjuna, he is also a living entity, we are also living entity. So we are also unhappy, because we are separated from Kṛṣṇa.
These modern philosophers or scientists, they may suggest that they may go on thinking otherwise that they can improve the world situation in their own way, but that is not possible. We are unhappy on account of being separated from Kṛṣṇa. They do not know that. Just like a child, a child is crying, nobody can say why he is crying, but actually a child is generally in crying condition being separated from the mother.