Bhagavad Gita · Chapter 1: Arjuna's Despair

Bhagavad Gita 1.37

tasmānnārhā vayaṃ hantuṃ dhārtarāṣṭrānsvabāndhavān | svajanaṃ hi kathaṃ hatvā sukhinaḥ syāma mādhava ||

So we ought not to kill the sons of Dhritarashtra, our own relatives. How could we ever be happy, Madhava, after killing our own people?

Modern context

Arjuna's test for the decision is: will we be happy afterwards? It is a natural question and not a sufficient one. Some duties leave us sad and are still ours to do. Krishna will offer another test: what does the situation rightly require of me?