When it is painful to remember the past, it is better to simply repent of what had been bad, and think no more about it. In order not to despair or be enfeebled by it, 'remember the examples of God's great mercies to great sinners. The main thing: do not condemn, do not envy, know yourself and be with God.'
In his famous book, 'The Ladder', St John Climacus records the life of this saint. The young Acacius was a novice with an evil elder in the monastery on Sinai. The foul-tempered elder daily groused and grumbled at Acacius, and often beat him, tormenting and ill-treating him in every possible way. Acacius did not complain, but bore it all patiently and with trust that it would work for his salvation. When anyone asked him how he survived, he replied : 'Well, as before the Lord God'. After nine years of obedience and ill-treatment, Acacius died. The elder buried him and then went off to lament to another elder, a holy man, saying: 'Acacius, my disciple, is dead. 'I don't believe it' replied the holy elder , 'Acacius is not dead.' They then both went to the dead man's grave, and the holy elder called out: 'Brother Acacius, are you dead?' The obedient Acacius, obedient even in death, replied: 'I am not dead; the obedient cannot die.' Then the evil elder repented and shut himself in a cell near Acacius's grave, where he spent the rest of his life in repentance and prayer.
A man may seem to be silent, but if his heart is condemning others, he is babbling ceaselessly. But there may be another who talks from morning till night and yet he is truly silent, that is, he says nothing that is not profitable.
The drunkard, the fornicator, the proud - he will receive God's mercy. But he who does not want to forgive, to excuse, to justify consciously, intentionally... that person closes himself to eternal life before God, and even more so in the present life. He is turned away and not heard.
Then we say: 'Forgive us our trespasses as we forgive those who trespass against us.' Brothers, praying thus, we should very much fear lest the Lord reply to these words of our prayer: 'The judgments you give are the judgments you will get, and the amount you measure out is the amount you will be given.' And you who ask this, see whether you did to no one what you did not want done to you. Therefore before we hear these words of the Lord, brethren, let us first examine our hearts as to whether we are with justice asking of the Lord what we have not denied to those asking us. We ask that our trespasses be forgiven us. God hears and He wants to forgive us, but only if we first pardon those who ask us to do likewise.