सुखदुःखे समे कृत्वा लाभालाभौ जयाजयौ। ततो युद्धाय युज्यस्व नैवं पापमवाप्स्यसि ॥

sukha-duḥkhe same kṛitvā lābhālābhau jayājayau tato yuddhāya yujyasva naivaṁ pāpam avāpsyasi

Taking as equal pleasure and pain, gain and loss, victory and defeat, gird thee for the battle; thus thou shalt not incur sin.

In plain words: Krishna tells Arjuna to treat pleasure and pain, gain and loss, winning and losing as the same. If he fights with this calm, steady mind, he will do no wrong.