The Buddha describes three cases where vigour should be applied.
“Tīhi, bhikkhave, ṭhānehi ātappaṁ karaṇīyaṁ. Katamehi tīhi? Anuppannānaṁ pāpakānaṁ akusalānaṁ dhammānaṁ anuppādāya ātappaṁ karaṇīyaṁ, anuppannānaṁ kusalānaṁ dhammānaṁ uppādāya ātappaṁ karaṇīyaṁ, uppannānaṁ sārīrikānaṁ vedanānaṁ dukkhānaṁ tibbānaṁ kharānaṁ kaṭukānaṁ asātānaṁ amanāpānaṁ pāṇaharānaṁ adhivāsanāya ātappaṁ karaṇīyaṁ. Imehi tīhi, bhikkhave, ṭhānehi ātappaṁ karaṇīyaṁ.
“Bhikkhus, in three cases, |vigour::effort, energy, and enthusiasm, lit. to be burned [ātappa]| should be applied. What three? 1) Vigour should be applied for the non-arising of unarisen |unwholesome::unhealthy, unskillful, unbeneficial, or karmically unprofitable [akusala]| mental qualities. 2) Vigour should be applied for the arising of unarisen |wholesome::healthy, beneficial, useful [kusalesu]| mental qualities. 3) Vigour should be applied for enduring arisen painful bodily feelings—those that are intense, harsh, sharp, disagreeable, unpleasant, and even life-threatening. In these three cases, bhikkhus, vigour should be applied.
Yato kho, bhikkhave, bhikkhu anuppannānaṁ pāpakānaṁ akusalānaṁ dhammānaṁ anuppādāya ātappaṁ karoti, anuppannānaṁ kusalānaṁ dhammānaṁ uppādāya ātappaṁ karoti, uppannānaṁ sārīrikānaṁ vedanānaṁ dukkhānaṁ tibbānaṁ kharānaṁ kaṭukānaṁ asātānaṁ amanāpānaṁ pāṇaharānaṁ adhivāsanāya ātappaṁ karoti. Ayaṁ vuccati, bhikkhave, bhikkhu ātāpī nipako sato sammā dukkhassa antakiriyāyā”ti.
Bhikkhus, when a bhikkhu applies vigour for the non-arising of unarisen unwholesome mental qualities, when he applies vigour for the arising of unarisen wholesome mental qualities, when he applies vigour for enduring arisen painful bodily feelings—those that are intense, harsh, sharp, disagreeable, unpleasant, and even life-threatening—then, bhikkhus, that bhikkhu is said to be |with continuous effort::ardent, zealous, with energy, with application [ātāpī]|, |prudent::sensible and careful when making judgments and decisions, astute, discerning [nipaka]|, and mindful, and working rightly to bring an end to |suffering::discomfort, unpleasantness, discontentment, dissatisfaction, stress, pain, disease, i.e. mild or intense suffering [dukkha]|.”
“Bhikkhus, in three cases, |vigour::effort, energy, and enthusiasm, lit. to be burned [ātappa]| should be applied. What three? 1) Vigour should be applied for the non-arising of unarisen |unwholesome::unhealthy, unskillful, unbeneficial, or karmically unprofitable [akusala]| mental qualities. 2) Vigour should be applied for the arising of unarisen |wholesome::healthy, beneficial, useful [kusalesu]| mental qualities. 3) Vigour should be applied for enduring arisen painful bodily feelings—those that are intense, harsh, sharp, disagreeable, unpleasant, and even life-threatening. In these three cases, bhikkhus, vigour should be applied.
Bhikkhus, when a bhikkhu applies vigour for the non-arising of unarisen unwholesome mental qualities, when he applies vigour for the arising of unarisen wholesome mental qualities, when he applies vigour for enduring arisen painful bodily feelings—those that are intense, harsh, sharp, disagreeable, unpleasant, and even life-threatening—then, bhikkhus, that bhikkhu is said to be |with continuous effort::ardent, zealous, with energy, with application [ātāpī]|, |prudent::sensible and careful when making judgments and decisions, astute, discerning [nipaka]|, and mindful, and working rightly to bring an end to |suffering::discomfort, unpleasantness, discontentment, dissatisfaction, stress, pain, disease, i.e. mild or intense suffering [dukkha]|.”
“Tīhi, bhikkhave, ṭhānehi ātappaṁ karaṇīyaṁ. Katamehi tīhi? Anuppannānaṁ pāpakānaṁ akusalānaṁ dhammānaṁ anuppādāya ātappaṁ karaṇīyaṁ, anuppannānaṁ kusalānaṁ dhammānaṁ uppādāya ātappaṁ karaṇīyaṁ, uppannānaṁ sārīrikānaṁ vedanānaṁ dukkhānaṁ tibbānaṁ kharānaṁ kaṭukānaṁ asātānaṁ amanāpānaṁ pāṇaharānaṁ adhivāsanāya ātappaṁ karaṇīyaṁ. Imehi tīhi, bhikkhave, ṭhānehi ātappaṁ karaṇīyaṁ.
Yato kho, bhikkhave, bhikkhu anuppannānaṁ pāpakānaṁ akusalānaṁ dhammānaṁ anuppādāya ātappaṁ karoti, anuppannānaṁ kusalānaṁ dhammānaṁ uppādāya ātappaṁ karoti, uppannānaṁ sārīrikānaṁ vedanānaṁ dukkhānaṁ tibbānaṁ kharānaṁ kaṭukānaṁ asātānaṁ amanāpānaṁ pāṇaharānaṁ adhivāsanāya ātappaṁ karoti. Ayaṁ vuccati, bhikkhave, bhikkhu ātāpī nipako sato sammā dukkhassa antakiriyāyā”ti.