Money alters the dynamic with people. It is here that it gets real complicated. When your income changes, your social network changes, too. Not always in an obvious manner, not always with purpose, but it does. Those who know your past life begin to stay away. The people in your new bracket have an assumption that you have not yet learned. Financial transition is lonely and no one speaks of it because it sounds ungrateful. How do you complain about problems that stemmed from more?
You are right about discipline when it comes to money. We need clarity in discipline, I think. It assumes that you know which are your true desires and which are the desires that your new environment created for you. And, most people cannot tell the difference until they have already committed. The spending was not reckless, but was justified in the context at the time.
This changes you mentioned when the financial life of people changes does not exist in the life of all, not that you can't actually experience that change in the lifes of people but some people still remains who they are even after been blessed financially.
I will say among everything on earth money is the only thing that changes people within the twinkle of an eye and never consider size while doing it but in the middle of 100, we can still find few that remains who they are no matter what.
This ability to remain neutral even with money can only be seen in people that has discipline and self-awareness