Therefore...
Therefore; all the detriments and afflictions resulting from the sinning characteristic of "pride" can apply to conceit, too; may Allah grant us refuge from it. FORGETTING ABOUT AND UNDERESTIMATING SINS Conceit causes one to forget many sins which he committed in the claim that he does not need to reform himself; so he does not mend what he had broken. As a result for this heedlessness, he forgets many sins, and he is not concerned about the sins which he still remembers.
This condition may drag one into committing new sins. Perhaps this is the meaning referred to in a tradition quoted in al-Shi'a From Imam al-Sadiq (a.s) who cites the Messenger of Allah (a.s) in a tradition in which Mousa (Moses) son of lmran (Amram) asks Satan.
"Tell me about the sin which, when a son of Adam commits, you overtake him." Satan said, "It is when he is proud of himself, thinks too much of his good deeds and his sin looks small in his eyes." It is known that when Satan overtakes someone, the result will be more sinning, in addition to underestimating the for this by itself is an insult to the status of the divine greatness which is one of the greatest sins, and it may stop one from being included in the divine mercy, as some traditions point out.
In the sacred book where Zaid the cooking oil seller cites Imam al-Sadiq (a.s) saying that Abu Abdullah said that he had heard Abu Muhammad (a.s) saying, "One of the sins which are not forgiven is when a man says, 'Blessed am I had I only not done anything other than this [deed ]!" Abu Hashim al-Ja'fari quotes Imam al-Hassan al-'Askari (a.s) saying that he heard Abu Muhammad (a.s) saying, "Among the sins that arc not forgiven is one saying, 'I wish I would not be held accountable except for only this [deed]!" Imam al-Khomeini, the mentor, may I be his sacrifice, has explained that conceit obliterates belief and ruins the rewards for the good deeds, according to a tradition narrated by Ali ibn Suwaid.
The imam was asked about the conceit that spoils good deeds, so the imam explained some of its degrees, citing other traditions as well, in this regard. He said the following : "The conceit tree is bad; its fruit is many major sins and abominations. When its root rests in the heart, one's affair is dragged into disbelief and shirk and more than both of these.
One of its consequences is underestimating sins; rather, one who is conceited is not in the process of reforming himself claims it is pure and purified.