It seems to me that personal finances should take a lot less time for someone who has a billion dollars vs. someone who has, say, $100k. The latter can lose it

It seems to me that personal finances should take a lot less time for someone who has a billion dollars vs. someone who has, say, $100k. The latter can lose it all on a bad financial decision, and probably has ideas for what they could do if only they could double or 10x or 100x the money, so risks can be worthwhile. The billionaire will keep getting richer beyond human comprehension even if they just put the entire fortune into treasury bonds. 4% interest on $1B is objectively so much money that you shouldn't bother trying to get more if there's anything else in your life that you'd rather spend time on. (Of course a lot of billionaires get there because the single one thing they want in life is to make money and see the number grow, but Cook doesn't seem that way.)