As time proceeds and children grow up, two new factors of great importance are liable to be added to those that determine the attitude of parents towards their children, although in many cases one or both of these factors may have been present in germinal form from the beginning. Both factors are connected with the biological truth that in the history of the race the child is the natural successor and substitute of the parent; but while having this much in common, they differ markedly in their psychological and social nature and effects, one factor tending to produce envy and hatred towards the children, the other love, pride and joy in their success. [Sidenote: Envy of childrens' superiority] The first of these two factors consists in the unwelcome realisation that the child will shortly be, or perhaps already is, the equal or even the superior of the parent in certain of the more important of life's aspects. Thus the father may become painfully aware of the fact that he is being gradually but certainly outmatched by his son in strength or skill or learning; while the mother may similarly find herself becoming outrivalled by her daughter in beauty, charm, accomplishments or intellectual power. This awareness on the parent's part of the increasing failure of their own powers relatively to those of their children is naturally liable to increase the bitterness that they may already feel towards their children for other reasons. Just as the self-interests of the parents formerly caused them to grudge the care, attention and effort which the existence of the children demanded, so now their pride and self-love may cause them to grudge their children that superiority which nature in the course of time bestows upon them. [Sidenote: Parents' identification of themselves with their children]