This material world is like the prison house of God; souls who have turned their backs towards Him have been put here. So, we cannot expect the people of this world to behave like saints. There will always be persons who will come to cheat us, and on some occasions, they may even succeed. That is life; we all get cheated once in a while. But the important thing is to learn to take it in our stride. That is where the quality of forgiveness comes in.
If we continue to harbor resentment towards those who have wronged us, we will be unable to progress spiritually. Resentment acts like a poison on the mind, filling it with bitterness. And we keep reliving the sour experience within, pinned down to the past. Someone aptly said: "Resentment is like taking poison and waiting for the other person to die."
On the spiritual path we must be careful nor to nurture ill feelings towards anyone, realizing that they will harm us more than anyone else. Jagadguru Shri Kripaluji Maharaj says:
भूलिहुँ दुर्भावना कहुँ, हो न सपनेहुँ प्यारे। (साधना करू प्यारे)
"Even in your dreams, do not make the mistake of harboring ill-will towards anyone."
Forgiveness is a sublime personality trait that immediately releases all bitterness from the mind. It is a favor we do, not to the other person, but to ourselves. The lives of saintly people are full of inspiring stories of how they forgave their wrongdoers, and even succeeded in winning them over by their love.