I think that is because people are in love. They are not in the mood to think about past mistakes. I remember a book I read years ago called Love and Limerance . Limerance was the crazy, in love, romantic feeling which usually fades with time. Love, as we know, is about deep caring, work, overcoming the selfish ego, appreciating the other, a kind of discipline.
Love is a big subject.
Perry and I read and learned from Harville Hendricks' book, Getting the Love You Want . This book explains the phenomenon of falling in love. I think the most important thing to understand about falling in love is that it happens when we find someone who somehow reminds us unconsciously of our early childhood caretakers. It is the familiarity that attracts us. The primal relationship and all its passions and comforts is called to the surface.