Some believers may think that the pain of regret for committing a sin is just discomfort that has no impacts; thus, they must let it go. However, this is a wrong notion, as there are notable impacts for going through such a pain. This is reflected in the concept of Tawba or repentance to Allah (s.w.t).
Repentance is regret over committing a sin, hence, it is vastly quoted that regret is repentance. It is evident that regret comes with the intention to stay away from the sin, thus the person who truly regrets committing a sin strives to correct his flaws. To do so, a believer must know that repentance is not just stating: “Astaghfir Allah” meaning I ask Allah to forgive me, but rather he must regret committing the sin and have an intention to fix his flaws and not to return to the sin.
A sinner must not fall into the despair of Allah and his mercy, because Allah loves those who repent and those who are pure. Imam Al-Sadiq(a.s) is quoted to have stated: "pondering an hour is better than worshipping a year". Thus what will help to leave a sin is to reflect on the greatness of Allah and his great right on our shoulders, and that he is watching, as reported in Nahj Al-Balaghah that Imam Ali(a.s) stated: "Beware of disobeying Allah in solitude, because the witness of that situation is also the judge."