"And what, monks, is right effort?

[i] "There is the case where a monk generates desire, endeavors, activates persistence, upholds & exerts his intent for the sake of the non-arising of evil, unskillful qualities that have not yet arisen.

[ii] "He generates desire, endeavors, activates persistence, upholds & exerts his intent for the sake of the abandonment of evil, unskillful qualities that have arisen.

[iii] "He generates desire, endeavors, activates persistence, upholds & exerts his intent for the sake of the arising of skillful qualities that have not yet arisen.

[iv] "He generates desire, endeavors, activates persistence, upholds & exerts his intent for the maintenance, non-confusion, increase, plenitude, development, & culmination of skillful qualities that have arisen: This, monks, is called right effort."

— SN 45.8

"Abandon what is unskillful, monks. It is possible to abandon what is unskillful. If it were not possible to abandon what is unskillful, I would not say to you, 'Abandon what is unskillful.' But because it is possible to abandon what is unskillful, I say to you, 'Abandon what is unskillful.' If this abandoning of what is unskillful were conducive to harm and pain, I would not say to you, 'Abandon what is unskillful.' But because this abandoning of what is unskillful is conducive to benefit and pleasure, I say to you, 'Abandon what is unskillful.'

"Develop what is skillful, monks. It is possible to develop what is skillful. If it were not possible to develop what is skillful, I would not say to you, 'Develop what is skillful.' But because it is possible to develop what is skillful, I say to you, 'Develop what is skillful.' If this development of what is skillful were conducive to harm and pain, I would not say to you, 'Develop what is skillful.' But because this development of what is skillful is conducive to benefit and pleasure, I say to you, 'Develop what is skillful.'"

— AN 2.19

"One tries to abandon wrong view & to enter into right view: This is one's right effort...

"One tries to abandon wrong resolve & to enter into right resolve: This is one's right effort...

"One tries to abandon wrong speech & to enter into right speech: This is one's right effort...

"One tries to abandon wrong action & to enter into right action: This is one's right effort...

"One tries to abandon wrong livelihood & to enter into right livelihood: This is one's right effort."

— MN 117

As Ven Sona was meditating in seclusion [after doing walking meditation until the skin of his soles was split & bleeding], this train of thought arose in his awareness: "Of the Blessed One's disciples who have aroused their persistence, I am one, but my mind is not released from the effluents through lack of clinging/sustenance. Now, my family has enough wealth that it would be possible to enjoy wealth & make merit. What if I were to disavow the training, return to the lower life, enjoy wealth, & make merit?"

Then the Blessed One, as soon as he perceived with his awareness the train of thought in Ven. Sona's awareness — as a strong man might stretch out his bent arm or bend his outstretched arm — disappeared from Vulture Peak Mountain, appeared in the Cool Wood right in front of Ven. Sona, and sat down on a prepared seat. Ven. Sona, after bowing down to the Blessed One, sat to one side. As he was sitting there, the Blessed One said to him, "Just now, as you were meditating in seclusion, didn't this train of thought appear to your awareness: 'Of the Blessed One's disciples who have aroused their persistence, I am one, but my mind is not released from the effluents... What if I were to disavow the training, return to the lower life, enjoy wealth, & make merit?'"

"Yes, lord."

"Now what do you think, Sona. Before, when you were a house-dweller, were you skilled at playing the vina?"

"Yes, lord."

"And what do you think: when the strings of your vina were too taut, was your vina in tune & playable?"

"No, lord."

"And what do you think: when the strings of your vina were too loose, was your vina in tune & playable?"

"No, lord."

"And what do you think: when the strings of your vina were neither too taut nor too loose, but tuned (lit: 'established') to be right on pitch, was your vina in tune & playable?"

"Yes, lord."

"In the same way, Sona, over-aroused persistence leads to restlessness, overly slack persistence leads to laziness. Thus you should determine the right pitch for your persistence, attune ('penetrate,' 'ferret out') the pitch of the [five] faculties [to that], and there pick up your theme."

"Yes, lord," Ven. Sona answered the Blessed One. Then, having given this exhortation to Ven. Sona, the Blessed One — as a strong man might stretch out his bent arm or bend his outstretched arm — disappeared from the Cool Wood and appeared on Vulture Peak Mountain.

So after that, Ven. Sona determined the right pitch for his persistence, attuned the pitch of the [five] faculties [to that], and there picked up his theme. Dwelling alone, secluded, heedful, ardent, & resolute, he in no long time reached & remained in the supreme goal of the holy life for which clansmen rightly go forth from home into homelessness, knowing & realizing it for himself in the here & now. He knew: "Birth is ended, the holy life fulfilled, the task done. There is nothing further for the sake of this world." And thus Ven. Sona became another one of the arahants.

— AN 6.55