I ask myself this question a lot, I know human greed is common (as seen by billionares who work their whole lives when they could have retired at 40 and live like gods)
Right now I think having around 5 million dollars invested in real estate and earning about $35k per month from it for the rest of my life without moving a single finger
would be enough for me to retire and live comfortably, travel the world, have any car I want and enjoy the good life, but maybe at that point I'll want private jets and yachts and other stuff
We'll first have to reach that point and see what happens haha