If you take 4% of somebody’s wealth, of course you are making their fortune smaller. Perhaps what you mean is that their fortunes would normally be growing at 4

If you take 4% of somebody’s wealth, of course you are making their fortune smaller. Perhaps what you mean is that their fortunes would normally be growing at 4% per year, so overall, they would not decrease. Maybe. I suspect that billionaire’s capital is rather mobile, though.