रजस्तमश्चाभिभूय सत्त्वं भवति भारत। रजः सत्त्वं तमश्चैव तमः सत्त्वं रजस्तथा ॥

rajas tamaśh chābhibhūya sattvaṁ bhavati bhārata rajaḥ sattvaṁ tamaśh chaiva tamaḥ sattvaṁ rajas tathā

Now Harmony prevaileth, having overpowered Motion and Inertia, O Bhârata; now Motion, having overpowered Harmony and Inertia; and now Inertia, having overpowered Harmony and Motion.

In plain words: Krishna says the three qualities keep competing inside us. Sometimes goodness wins over the other two, sometimes passion wins, and sometimes dullness wins.