Not losing hope for Allah's mercy

In many verses of the Qur'an, Allah mentions that Muslims—even
those with the most fear of Allah—– may make mistakes. In one verse,
Allah reveals;
Say [from Me]: 'My servants, you who have transgressed against
yourselves, do not despair of the mercy of Allah. Truly Allah
forgives all wrong actions. He is the Ever-Forgiving, the Most
Merciful.' " (Surat az-Zumar; 53)
It surely brings relief to their hearts, for a believer who errs
could feel great regret, sorrow and guilt.
Allah has made the scope for error so wide in human beings that He
has promised to forgive a person's errors without exception, if
that person is sorry and repents of what he has done.
But despite of the many consolations in the Qur'an that refresh the
spirit and give hope, many human beings do not admit that they make
mistakes. In spite of the glad tidings announced in the Qur'an,
after making a mistake they become wrapped in despair and become
anxious and downhearted.
An individual who refuses to acknowledge errors he has committed
out of pride and arrogance is greatly saddened by what he has done.
He has trouble accepting that he is a creature prone to making
mistakes and faulty decisions, and whose actions and words may be
wrong.
He does not consider that perfection and freedom from error belong
only to Allah. He wants to be perfect himself. But he cannot, and
the fact that some of his attitudes are wrong (despite his desire
that they not be), draws him into despair.
A believer experiences deep peace by accepting his imperfections and
helplessness in relation to Allah and never claims to be free from
error.
It should be remembered that the tendency to err and sin—even
though one may be a firm believer —makes him more aware of Allah's
perfection. One can conceive of perfection only when he had
experienced imperfection.
Consciousness of his own failures and weaknesses lets him better
appreciate the absolute perfection of Allah.