The Buddha explains how to overcome complacency and doubt by guarding the sense faculties, applying moderation in eating, being dedicated to wakefulness, developing insight into wholesome qualities, and engaging in the development of the awakening factors during the first and last watch of the night.

Upajjhāya sutta - Mentor

Then, a certain bhikkhu approached his own preceptor and said: "Venerable sir, at present I feel as if my body is intoxicated, the directions seem unclear to me, the teachings do not spring to mind, complacency completely occupies my mind, I do not find enjoyment in the spiritual life, and I have doubts about the teachings."

Then the preceptor taking his pupil with him, approached the Blessed One. After paying respects to the Blessed One, they sat down to one side. Once seated, the preceptor said to the Blessed One: "Venerable sir, this bhikkhu says: 'At present, I feel as if my body is intoxicated, the directions seem unclear to me, the teachings do not spring to mind, complacency completely occupies my mind, I do not find enjoyment in the spiritual life, and I have doubts about the teachings.'"

The Blessed One replied: "Indeed, bhikkhu, this happens when 1) one is not guarded in the sense faculties, 2) not applying moderation in eating, 3) not dedicated to wakefulness, 4) lacks insight into wholesome qualities, and 5) does not engage in the development of the awakening factors during the first and last watch of the night. As a result, the body feels as if intoxicated, the directions seem unclear, the teachings do not spring to mind, complacency completely occupies the mind, one does not find enjoyment in the spiritual life, and doubts about the teachings arise.

Therefore, bhikkhu, you should train yourself thus: 'I will be guarded in the sense faculties, apply moderation in eating, be dedicated to wakefulness, develop insight into wholesome qualities, and engage in the development of the awakening factors during the first and last watch of the night.' This is how you should train yourself."

Then, that bhikkhu, having been instructed by the Blessed One with this advice, rose from his seat, paid respects to the Blessed One, circumambulated him to the right, and departed.

Thereafter, that bhikkhu, living in seclusion, with diligence, continuous effort, and resoluteness, not long after, realized by personal knowledge and attained in that very life the unsurpassed culmination of the spiritual life for which sons of good families rightly go forth from the household life into homelessness.

He understood: "Birth is ended, the spiritual life has been lived, what had to be done has been done, there is no more coming to any state of being." And that bhikkhu became one among the arahants.

Then that bhikkhu, having attained arahantship, approached his preceptor and said: "Venerable sir, at present my body no longer feels as if intoxicated, the directions are clear to me, the teachings spring to mind, complacency no longer occupies my mind, I find enjoyment in the spiritual life, and I have no doubts about the teachings."

Then, taking his pupil with him, the preceptor approached the Blessed One. After paying respects to the Blessed One, they sat down to one side. Once seated, the preceptor said to the Blessed One: "Venerable sir, this bhikkhu says: 'At present, my body no longer feels as if intoxicated, the directions are clear to me, the teachings spring to mind, complacency no longer occupies my mind, I find enjoyment in the spiritual life, and I have no doubts about the teachings.'"

The Blessed One replied: "Indeed, bhikkhu, this happens when 1) one is guarded in the sense faculties, 2) applies moderation in eating, 3) is dedicated to wakefulness, 4) has insight into wholesome qualities, and 5) engages in the development of the awakening factors during the first and last watch of the night. As a result, the body does not feel as if intoxicated, the directions are clear, the teachings spring to mind, complacency does not occupy the mind, one finds enjoyment in the spiritual life, and there are no doubts about the teachings.

Therefore, bhikkhus, you should train yourselves thus: 'We will be guarded in the sense faculties, apply moderation in eating, be dedicated to wakefulness, develop insight into wholesome qualities, and engage in the development of the awakening factors during the first and last watch of the night.' This is how you should train yourselves."