This aphorism means that “injuries” (which can be related to problems, disagreements, a harmful or painful situation) can be easily disappear just as dust do with a simple puff of air). On the other hand, the benefits you get by experiencing a conflict or a worrying situation will last for ever in the same way a craftsman caves into marble. All in all, people should look at the good side of things rather than the negative ones.
Precisely the author keeps the interest of readers not describing clearly the kind of relationship in Giselle's family. By doing this, readers had to imagine and assume how it was. Instead, the author described better scenes with Dark Star and the influence of books about horses in Giselle's life and actions. Also the fact that she broke her arm but not referring to it in detail leads the readers to imagine and guess what could have occurred.