I would expect more than 90% of the people to spend most of what they make every month and require another paycheck to continue going.

After all, if you don't have to do that, then you might as well retire, right?

So 40% of people can skip a few paychecks and not dip into a rainy day fund, somehow, that seems pretty doggone good

I think there is a huge difference between “can miss a few paychecks” and “can retire” (aka “never need a paycheck again”).

Yeah this does lend to a lot of nuance. Modern financial systems allow for pretty quick liquidity. It’s probably best to invest everything, charge expenses on a credit card, then pay off the credit card at the end of the month, keeping your checking account rather sparse. Taking full advantage of the float as they say.