Until you have it, you don't really understand the magnitude of sustaining that wealth. This includes the ability to replace money as it gets spent.
To have true wealth is the ability to hold onto it. It's so easy to lose it all whether it's because you overspend, made bad investments, or fell upon a situation where you had to fork over a large chunk of your savings.
Once you're able to successfully make money in your sleep and more importantly, make money as money also goes out the door, the next challenge is how this wealth is going to stay in your family long after you're gone. Again, it is very easy for the descendants to squander it all.