AN 1.41

“Bhikkhus, suppose there is a misdirected spike of rice or barley, and it is pressed by the hand or foot. It is impossible for it to pierce the hand or foot and draw blood. Why is that? Because the spike is misdirected. In the same way, it is impossible for a bhikkhu with a misdirected mind to pierce ignorance, arouse true wisdom, and realize Nibbāna. Why is that? Because the mind is misdirected.”

AN 1.42

“Bhikkhus, suppose there is a well-directed spike of rice or barley, and it is pressed by the hand or foot. It is possible for it to pierce the hand or foot and draw blood. Why is that? Because the spike is well-directed. In the same way, it is possible for a bhikkhu with a well-directed mind to pierce ignorance, arouse true wisdom, and realize Nibbāna. Why is that? Because the mind is well-directed.”

Related Teachings:

Tracing the causes of ignorance | delusion | avijjā sutta (AN 10.61) - Even though ignorance has no discernible first point, it still has a cause.

The Cave of Ignorance (Snp 4.2) - Vivid verses on overcoming the mire of delusion by avoiding attachment to sensory pleasures, discerning their causes, and practicing for being free of ‘mine’.