That's true -- but the top is a harder place to stay at than you think. China, the West, and the Middle East all have variations of "from shirtsleeves to shirts

That's true -- but the top is a harder place to stay at than you think. China, the West, and the Middle East all have variations of "from shirtsleeves to shirtsleeves in three generations"; most fortunes don't last past the grandchildren of the people who earned them -- and this was even true under feudalism, where new titles had to be continually granted, and the fourth generation after the man who was first granted arms was hardly ever armigerous, if it existed at all. The few who make it past the third generation, generally continue on indefinitely (the Roosevelts, who bought a 40-acre farm on Manhattan Island in the 1600s and still own it today, should come to mind; likewise the Rothschilds and Rockefellers in more recent times); but getting over that three-generation hurdle is a formidable task.