I think because he looks at it as more of a risk as to whether or not you will actually make money on it when you go to sell it, which is different from a specific long-term investment in real estate (statistics are something like the average American movies 11 times in their lifetime). Plus when you couple in the cost of running a house (property taxes, homeowner's insurance, replacement parts like broken windows or defective water heaters, maintenance equipment like lawnmowers, repair costs - especially for emergencies like burst pipes, monthly utility bills, etc.), it's not like it's a business you own & operate where you put money in & make an ongoing profit, it's a diceroll as to whether or not you'll get a profit after the accumulated maintenance cost during all of those years of owning & operating your live-in residential home, unlike a business where you lease or buy a space and use that to generate money to cover that cost. Which is why it's such a big point of contention defining it that way in the financial community. From the author's perspective, you're paying money every month to keep that home & do the upkeep on it, therefore per his definition being a liability being anything you have that costs you money, it is a liability, not an asset. Personally, I prefer to look at it that way too, because it's not a guaranteed thing like bank interest or stock dividends - because if you're say forced to relocate due to a job change and it's a buyer's market, then you stand to lose money, but meanwhile, every day, week, monthly, and year that you live in that house, it's cost you money out of pocket to stay there.