Hahahaha....
I think this thread took a couple of sudden unexpected turns by WineRose
The way I took it in, while I haven't watched the movie and not familiar with its plot but assume it's some kind of love story, is that when two are in love, there's no need to say sorry because the act that would normally prompt an apology was not intended/intentional. And not noticing the hair cut example, while I see your point, you are not in love with her if you don't notice your gf/wife's hair cut, period, thus, it's a deeper issue than having to say sorry for hurting other's feeling.
When two are in love... I mean in love where one gives everything and vice versa
When everything you do you say you think is for that person only
The other person would just know why there was this "hurtful" act or omission of it, which would hurt the person's feeling typically, but not to the person because he/she would just know it was not intended. And can actually smile about it, knowing it was a byproduct of him/her loving wholeheartedly.