The last of the imperfections (defilements) of the mind is negligence. The Pali word is pamāda, meaning heedlessness or negligence. It’s opposite is appamāda, meaning heedfulness, diligence, or zeal — the cornerstone of all skillful mental states.
So to counteract negligence, diligence must be applied to all of the previously mentioned defilements of the mind. If we are diligent, we know when the imperfections are present and we can look for ways to work with them so they don’t overwhelm us. If we are negligent, the defilements use our minds as playgrounds. Every time we interrupt or block a defilement, we strengthen our wisdom. Every time we allow a defilement to roam freely in our minds, that defilement is strengthened.
Vigilance is the path to the Deathless,
Negligence the path to death.
The vigilant do not die;
The negligent are as if already dead. (21)
Through effort, vigilance,
Restraint, and self-control,
The wise person can become an island
No flood will overwhelm. (25)
Unwise, foolish people
Give themselves over to negligence.
The wise
Protect vigilance as the greatest treasure. (26)
– Dhammapada verses, translated by Gil Fronsdal
The Buddha praised diligence for its ability to support the essential ingredients of awakening, the five spiritual faculties:
Bhikkhus, when a bhikkhu is established in one thing, the five faculties are developed, well developed in him. In what one thing? In diligence.
And what, bikkhus, is diligence? Here, bhikkhus, a bhikkhu guards the mind against the taints and against tainted states. While he is guarding the mind thus, the faculty of faith goes to fulfilment by development; the faculty of energy…the faculty of mindfulness…the faculty of concentration…the faculty of wisdom goes to fulfilment by development.
It is in this way, bhikkhus, that when a bhikkhu is established in one thing, the five faculties are developed, well developed in him.
– SN 48.56, translated by Bhikkhu Bodhi
So, the mental activity of “guarding the mind” is key to making progress against our own defilements. When we bring this knowledge to mind again and again, we are doing the work of awakening.
The Buddha’s final words in this world were about diligence:
All conditioned things are subject to decay. Strive on with heedfulness.
– from DN 16, translated by John Kelly

Imperfections that defile the mind:
(1) covetousness and unrighteous greed
(2) ill will
(3) anger
(4) revenge
(5) contempt
(6) a domineering attitude
(7) envy
(8) avarice
(9) deceit
(10) fraud
(11) obstinacy
(12) presumption
(13) conceit (māna)
(14) arrogance
(15) vanity
(16) negligence
from MN7, translated by Bhikkhu Nanamoli and Bhikkhu Bodhi