I'd heard about Millionaire Next Door for years and mistakenly wrote it off as one of those scammy "buy my program" books about visualization.
Then it was gifted to me, and boy, was I wrong! Couldn't put it down. It's packed full of interesting tidbits and data. While I'd highly recommend reading the book yourself, I also wrote some notes on it here [0].
I'd love to see these same studies, but updated to 2021.
I've got good news for you! There was another book written 2 years ago called Everyday Millionaires by Chris Hogan that conducted a new study of millionaires. I think MND studied 100 millionaires, while EM studied 10000.
Then it was gifted to me, and boy, was I wrong! Couldn't put it down. It's packed full of interesting tidbits and data. While I'd highly recommend reading the book yourself, I also wrote some notes on it here [0].
I'd love to see these same studies, but updated to 2021.
[0]: https://mtm.dev/millionaire-next-door