Hazrat Hakeemul Ummat Moulana Ashraf Ali Thanvi ra said: 

One must forget the mistakes of the past. It is one of the big errors that one speculates about the future based on past happenings. That is, one considers that I will be negligent in future also, as I have been in my life previously. This destroys the determination (to rectify and progress).

Moreover, during the rectification (islah) phase if one slips or commits a mistake it is inappropriate to contemplate (muraqabah) on it for forever. One should repent sincerely by saying “O Allah SWT, forgive me” and proceed forwards. Otherwise this will become a muraqabah of one’s own (faults that leads to decreasing determination as said above.) And the witnessing (mushahida) of Allah SWT(‘s benevolence & mercy, which is the goal and leads to His love) does not take place. 

(Basair-e-Hakeemul-Ummat 539)

صوفی نہ شود صافی تا دُر نہ کشد جامی
بسیار- سفر باید- تا- پختہ شود- خامی
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