Bhagavad Gita 2.11 · Ashochyan Anvashochas Tvamश्री भगवानुवाच अशोच्यानन्वशोचस्त्वं प्रज्ञावादांश्च भाषसे।गतासूनगतासूंश्च नानुशोचन्ति पण्डिताः ॥

-- The philosophy of the Gita begins from this verse.Bhishma and Drona deserve no grief because they are eternal in their real nature and they are virtuous men who possess very good conduct. Though you speak words of wisdom, you are unwise because you grieve for those who are really eternal and who deserve no grief. They who are endowed with the knowledge of the Self are wise men. They will not grieve for the living or for the dead because they know well that the Self is immortal and that It is unborn. They also know that there is no such a thing as death, that it is a separation of the astral body from the physical, that death is nothing more than a disintegration of matter and that the five elements of which the body is composed return to their source. Arjuna had forgotten the eternal nature of the Soul and the changing nature of the body. Because of his ignorance, he began to act as if the temporary relations with kinsmen, teachers, etc., were permanent. He forgot that his relations with this world in his present life were the results of past actions. These, when exhausted, end all relationship and new ones ones crop up when one takes on another body.The result of past actions is known as karm and that portion of the karma which gave rise to the present incarnation is known as prarabdha karma.