In an essay entitled On Forgiveness C. S. Lewis explains the difference between asking for forgiveness and giving an excuse. He explains that forgiving says "Yes, you have done this thing, but I accept your apology; I will never hold it against you and everything between the two of us will be exactly as it was before", but excusing says "I see that you couldn't help it or didn't mean it; you weren't really to blame."
When someone acts in a way that hurts us it may be helpful to think about why they did what they did. We may see some excuses for their behaviour. But generally those excuses will not provide full justification for what they have done. The remainder we need to forgive. That's what makes forgiveness so difficult.
even if he is absolutely fully to blame we still have to forgive him; and even if ninety-nine percent of his apparent guilt can be explained away by really good excuses, the problem of forgiveness begins with the one percent of guilt which is left over. To excuse what can really produce good excuses is not Christian charity, it is only fairness. To be a Christian means to forgive the inexcusable, because God has forgiven the inexcusable in you.