Bhagavad Gita · Sankhya YogaChapter 2, Shloka 14 (2.14)

The source of pleasure and pain. Krishna gives a simple analysis: cold and heat, pleasure and pain — all these arise from the contact of the senses with their objects. The self is not their source.

Two qualities: "āgamāpāyinaḥ" and "anityāḥ". These experiences come and go — and so they are impermanent. Shankaracharya makes a subtle point: why mention cold and heat separately? Because cold sometimes gives pleasure and sometimes pain — their nature is not fixed; whereas the nature of pleasure and pain is fixed.

"Titikṣasva" — endure. Shankaracharya: teṣu harṣaṃ viṣādaṃ vā mā kārṣīḥ — "do not feel elation or dejection in them." Ramanuja: endure with fortitude until the scripturally enjoined action, such as the war, is completed — that is, endurance for the sake of doing one's duty.

In Arjuna's context. The wounds of weapons in battle, the grief of the death of one's own people — all these are experiences that "come and go". Krishna does not deny them — he says "endure them".