To hurt, or injure, or do some injustice to another human being (or any other part of the creation) is not natural to man, but an aberration, a corruption, an infection upon the original and essential participation in the Image of God. Even sin, with its disastrous and cosmic effects, could not destroy the nature with which God made us. It can pervert, and misdirect, and even make it seem that sin is the truly natural thing (woe to us if we believe that lie!), but it can not obliterate God's good design.
This does not mean, however, that man makes "inherently" good choices (this is, in fact, one of the great theological non sequiturs of our recent history): without the grace and glory of God indwelling and pervading us, even our attempts at good cause harm. Two examples will have to suffice for now.
The ALS Bucket Challenge has raised a wonderful amount of awareness and not a small amount of money for research. However, in a world that so often hurts for water, how shall we justify our actions? (One friend I have went further and asked how we justify swimming pools; the point is well taken.) We are required to make what St Maximos calls a "gnomic" choice, an action of will in which there is no immediate right answer, but pragmatic or other factors than the Kingdom of God have full sway.
The other example, and I am going to be somewhat oblique about it, is when the financial stability of an institution requires the termination of employment for some workers (usually, as the case goes, those on the bottom rungs of the ladder, who are often the most financially vulnerable). To cause good, we cause great harm.
Let us now imagine that we have been hurt in some way: the reaction we have (remembering that our reactions, because of sin, act unnaturally, but also retain some connection and reflection to our original state) is protests of unfairness, injustice, or undue malice. Most likely, we will get at turns angry and depressed and so on. This leads us to the next stage: the judgment of the injurer. They are bad people, evil people, greedy people, etc. The use of the adjectival modifier, though, is not meant to describe the actions of the person, but their very nature: this is why we find it so hard to believe apologies or repentance, for how can anyone really change? It may be that the characteristic actions of a person are those called avarice, fair enough. But what modifier have we, unconsciously, chosen for ourselves? We are unforgiving. While we may have been hurt, and often badly and sometimes irreparably, the damage inflicted upon our souls and therefore the world by not forgiving is infinitely greater than any earthly injustice. "Fear not him who can kill the body, but rather him who can cast both body and soul into Gehenna." I've heard many interpretations of this passage, some saying the truly fearful one is Satan, some saying it is Christ, but the truly fearful one, the one St Augustine calls "nothing but a guide to my own self-destruction" is me. Christ gives us the prayer to "forgive us our trespasses, as we forgive those who trespass against us" for "if you do not forgive others their trespasses, neither will your Heavenly Father forgive you." To be unforgiving, to remember wrongs, to not seek reconciliation is to already be cast into Gehenna in the here-and-now, with the fullness thereof to be revealed later. To be forgiving is to be like God, so that forgiveness is His Image. By forgiveness we overcome the corrupting influences of sin: the Cross opens up the possibility to us, forgiveness is not something we do on our own.
Having this mind like Christ, we can see those who hurt us not as monsters, but as brothers and sisters (due to their shared humanity, not necessarily their faith) in need of the healing of Christ as we are in need of healing. St James tells us "