Nicholas, unlike his sister, is afraid. The mother has to comfort Nicholas every time his sister scares him. Having to comfort him takes a lot of her energy and attention. For example, you might see this attention when he hears a baby crying and runs around the house checking on both children. This shows that he has this concern for his children, you can see it from the fear on his face, and his rush to control them has an impact on his mental state. Having to often rush to his rescue for fear that something might happen to him would make the mother worry about his well-being since she cannot protect herself. Always being there for his son would also increase Nicholas' dependence on Grace as he would not learn to deal with problems on his own. Always being there for him and keeping him from learning how to face his fear is bad for both people, and it wears on both Nicholas and Grace.