Jesus answered, “I tell you, not seven times, but seventy-seven times.' Matthew 18.22
What Jesus says in answer to Peter's question about how often one should forgive someone else, is not to be taken as a precise number but as an exponential number. In other words one should not put a cap on forgiveness. Or, to put it yet another way, one is never justified in saying: I have reached the limit, I am now free not to forgive!
This is radical. Until this point, the morality surrounding forgiveness was more frugal: once was enough, three times was generous, seven times was stretching it. But Jesus came to remove all such restrictions, providing for the forgiveness of everyone by offering his perfect life as a ransom for the sins of the world. That put us all in his debt - a debt which he cancelled by forgiving us, thus blowing retribution out of the water - at least as a morally justifiable principle.
None of this is to say that forgiveness is easy. We struggle to forgive one another, especially when we feel hard done by. We even struggle to forgive God when we see - or even experience - undeserved suffering. This is natural because we are dealing with real feelings and life is precious and fairness matters.
The forgiveness Jesus gives and demands that we share nevertheless helps us put our own injuries into perspective. It is no quick fix but it does give us a framework for dealing with the issue: God's forgiveness of our sins through his death on the cross paves our way to eternal life even though we do not deserve it, so who are we to resent the lesser injuries whose impact is restricted to our temporary mortal lives?