Bhagavad Gita · Chapter 2: The Path of Understanding

Bhagavad Gita 2.33

atha cettvamimaṃ dharmyaṃ saṃgrāmaṃ na kariṣyasi | tataḥ svadharmaṃ kīrtiṃ ca hitvā pāpamavāpsyasi ||

But if you will not fight this righteous battle, then, having abandoned your duty and your honour, you will incur sin.

Modern context

Arjuna feared that fighting would be a sin. Krishna turns it round: failing to do what is rightly yours is also a wrong. We tend to count only the harm we cause by acting. The harm caused by standing aside when we were needed is just as real.