[12] And how, bhikkhus, is exertion fruitful, how is striving fruitful? Here, bhikkhus, a bhikkhu does not overwhelm himself with suffering (dukkha) when he is not already overwhelmed by suffering; he does not relinquish pleasure that accords with the Dhamma, yet he is not infatuated with that pleasure. He understands thus: 'As I strive with determined effort (saṅkhāra), there comes to be, through that determined striving, the fading away (virāga) of this source of suffering; but as I look on with equanimity (upekkhā), developing equanimity, there comes to be the fading away of this other source of suffering.' So, with regard to that source of suffering whose fading away comes about for him as he strives with determined effort, through that determined striving, he strives there with determined effort; and with regard to that source of suffering whose fading away comes about for him as he looks on with equanimity, developing equanimity, he develops equanimity there. As he strives with determined effort, there comes to be, through that determined striving, the fading away of this or that source of suffering—thus too that suffering (dukkha) is worn away for him; as he looks on with equanimity, developing equanimity, there comes to be the fading away of this or that source of suffering—thus too that suffering is worn away for him.
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.