funny, but I do know a foot doctor,

retire now after 30 some years, he said he make most his money not from the practic, but RE and banking, he once had bunch of medical buildings leased to other doctors.
In the mid 80, he went open up a bank, he said he didn't feel like borrow any more money from others, later the bank got bought out, he said he owns 10% of the bank at that time.
he sold his practic and all the RE about 4 years ago, his day job is like 小小石头, trading stock and play golf all over the world.