That part is key. It's really a combo of working hard in some way during strong economic times. You can do it in a down market but it's much more difficult. Building generational wealth in the 1950s was much easier than in the 1850s or than it will be in the 2050s, for example. If this isn't true, I'd like to institute a 100% inheritance tax and see how well someone like Meghan McCain or Paris Hilton fares against the rest of us.
My credentials in this.. my family did the exact story described here. Post-WW2 American family that built out an excavating company into a multimillion dollar empire that now includes a chain of banks and other side businesses. My wife's family, same thing but in the textile industry in Latin America. We were both tossed out, because our families are full of psychopaths and horrendous behavior, and we're actually decent folk who won't murder you for a larger inheritance (yes, it's happened in our families). So we never received any assistance, in fact, far less than even a normal, loving family of meager means would give their kids. She's out of her father's will because he blames her for his divorce, a 13 year old daughter at the time of his infidelity, and I'm expecting my brother and aunt to rob my parents blind. We have our own small side businesses but I'm currently hunting for a fulltime job and my wife is a public school teacher. From what I've seen in my life so far, I've never seen money do any good for anyone outside of basic needs. Maybe in the hands of a really wise, smart individual but that's tough to find and a fool is born every minute.
Working hard part is important and is before. Because if you get lucky first, you will lose it all and likely won't know what areas to take risks in.