Thoughts on investing with borrowed hard money?

[Nirzhar Kar]

Anyone invest by boring hard money and flipping more houses? I am starting my venture into flipping but  i wonder how people have 12+ houses at once without borrowing money? And since most good deals are cash, i am guessing that borrowing hard money is the only way to do this. Do people make a living by borrowing hard money and flipping or do they all do this with their own money by just slowly increasing their bankroll by flipping?