It is clear that when we consider the hopes that both Dexter Fletcher and his creator, F. Scott Fitzgerald, have for their children, their is a significant difference in the kind of lives they want for them. Dexter Fletcher for example makes it obvious that, although he recognises that his middle-class background actually gives him a certain advantage over his upper-class contemporaries, he wants his children to be born into wealth and social position rather than to have to earn it for themselves as he has had to:
He had seen that, in one sense, he was better than these men. He was newer and stronger. Yet in acknowledging to himself that he wished his children to be like them he was admitting that he was but the rough, strong stuff from which they eternally sprang.
Such a wish appears initially to be paradoxical until we realise the way that those born into wealth and social prestige were considered as being "better" socially than those who had earned their own way into the halls of the rich and famous.
However, considering F. Scott Fitzgerald's advice to his daughter as expressed in his letter, it is clear that he has very different wishes for his daughter, built around a life that is characterised by health, duty and courage:
All I believe in in life is the rewards for virtue (according to your talents) and the punishments for not fulfilling your duties, which are doubly costly.
There is no mention made of an inherited social position which is a birthright. Reference to concepts such as "virtue" immediately separate it from the kind of life that Dexter Fletcher wants his children to inherit.