All one's activities in a life devoid of Krsna consciousness simply lead to defeat and misuse of one's life. Naturally one who comes to Krsna consciousness regrets his previous sinful activities in the human form
SB Canto 4
The King, with aggrieved mind, began to speak to his wife with very pleasing words. Although he was filled with regret and tried to pacify her, he could not see any symptom of anger caused by love within the heart of his beloved wife.
The King very much regretted having left his Queen and having gone to the forest to execute sinful activities. When a person regrets his sinful activities, the abandoning of Kṛṣṇa consciousness and good intelligence, his path of deliverance from the path of material clutches is opened. As stated in Śrīmad-Bhāgavatam (5.5.5): parābhavas tāvad abodha jāto yāvan na jijñāsata ātma-tattvam. When a person loses his Kṛṣṇa consciousness and loses interest in self-realization, he must engage in sinful activities. All one's activities in a life devoid of Kṛṣṇa consciousness simply lead to defeat and misuse of one's life. Naturally one who comes to Kṛṣṇa consciousness regrets his previous sinful activities in the human form. Only by this process can one be delivered from the clutches of nescience or ignorance in materialistic life.