According to Osho, forgiving is hard because the ego feeds on misery and negativity; it survives by clinging to wounds, exaggerating hurts, and saying 'no.' Effortful forgiving only represses and can even inflate ego pride ('I forgave'). Real release comes from seeing the mind’s absurd game, accepting one's ordinariness, and shifting attention from thorns to roses; then the ego thins, bliss returns, and forgetting happens naturally.
We hold on to hurt because our ego enjoys the drama; once we see this silly habit and stop feeding it, letting go and forgetting happen by themselves.