Was Nathaniel adopted by a rich family?
I think so... I think they would have to be 'wealthy' for the movie to work but they are PROBABLY rich monetarily (not just spiritually wealthy) too when you think all those people are living in a house that's probably been paid off forever, they could easily save money well...
And then when his wife comes back to him after seeing how his family invested funds (smart lady - it's true love but it's not stupid) it just gets kind of hard to believe that his bro got this money and just knew how to invest it right away... when you get into that stuff it is expected that you lose first before you win...
When you look at the first point, it's not that strong.... But when you think about the second point with the first point it is more likely than not that he came from money but the parents wanted him to understand basic principles of *wealth creation* because that creates the feelings more than money. Therefore he did not know he was rich, but acted wealthy, and that gave him the creative power for the money to come to him...