Sometimes an easy forgiveness allows people to do the same mistake again and again.. May be because it gives a feeling that "anyway I will be excused, so why to worry..!" I tend to think that if someone gets an excuse easily even before they really feel guilty about what they have done or said, it seems that there is no way that they are going to correct themselves. Probably because the situation is easily handled for them and they are not given a chance to sit_and_think about what they have done and why they shouldn't be repeating it again.
When there are people who take even an excuse (by excuse, I mean both forgiveness and exceptional 'its ok' for what they have done/said), which they get after a lots of effort, as take it for granted; it doesn't surprise to say that people might treat an easy excuse as a cakewalk most of the times. I believe people correct themselves only when they internally realize what they have done/said and really feel for it.
I think that sometimes tolerating or forgiving someone's _not_so_nice_action_ is resulting in them not to realize how it affects/hurts someone else's feelings. Soft spoken words of "its ok, dear" with a gentle smile never means that you are allowed to repeat it again. It never means that it is any less pain or suffering for someone. It just means that sometimes the other person doesn't want you to know how much wrong you are, just for the fact that you shouldn't feel guilty about what you have done/said. It is simply because they care for you. But that doesn't mean that you can do/say the same thing again and say "i'm so sorry.. i didn't mean it this time too..' with an innocent smile!!
Remember that you are innocent only the first time. Next time, you pretty much know what you are doing/saying.