NEVER GIVE UP - TWO QUALITIES: Discontent with regard to skillful qualities & Unrelenting exertion

Aṅguttara Nikāya - Book of the Twos
Sutta No. 5: Relentlessly ( Upaññātasutta )

“Monks, I have known two qualities through experience: discontent with regard to skillful qualities and unrelenting exertion.”

“Relentlessly I exerted myself, [thinking,] ‘Gladly would I let the flesh & blood in my body dry up, leaving just the skin, tendons, & bones, but if I have not attained what can be reached through human firmness, human persistence, human striving, there will be no relaxing my persistence.’ From this heedfulness of mine was attained Awakening. From this heedfulness of mine was attained the unexcelled freedom from bondage.

“You, too, monks, should relentlessly exert yourselves, [thinking,] ‘Gladly would we let the flesh & blood in our bodies dry up, leaving just the skin, tendons, & bones, but if we have not attained what can be reached through human firmness, human persistence, human striving, there will be no relaxing our persistence.’ You, too, in no long time will reach & remain in the supreme goal of the holy life for which clansmen rightly go forth from home into homelessness, knowing & realizing it for yourselves in the here & now.

“Thus you should train yourselves: ‘We will relentlessly exert ourselves, [thinking,] “Gladly would we let the flesh & blood in our bodies dry up, leaving just the skin, tendons, & bones, but if we have not attained what can be reached through human firmness, human persistence, human striving, there will be no relaxing our persistence."’ That’s how you should train yourselves.”