Bhagavad Gita 18.59
यदहङ्कारमाश्रित्य न योत्स्य इति मन्यसे । मिथ्यैष व्यवसायस्ते प्रकृतिस्त्वां नियोक्ष्यति ॥
yad ahaṅkāram āśritya na yotsya iti manyase / mithyaiṣa vyavasāyas te prakṛtis tvāṃ niyokṣyati
Translation
If, taking refuge in ego, you decide I will not fight, that resolve is in vain. Nature will compel you.
Reflection
Which decision of yours from ego do you suspect your nature is going to override anyway?
Read this verse in its chapter: Chapter Eighteen
A precise psychological forecast. If Arjuna stays in the ahankara position and decides na yotsye, I will not fight, that decision will not hold. Mithyaisha vyavasaya, the resolve is empty. Prakriti, his own nature, the same nature that has made him a warrior, will yoke him back. The teacher is saying, you can pretend the decision is yours to make from ego, but the deeper engine of svabhava is going to run its course regardless. The ego's freedom of refusal is illusory. The actual question is not whether action will happen but in what spirit. The next verse confirms the inevitability.