rates never changing. Things like inheriting money or getting a bonus or refinancing which are fairly common over a 30 year mortgage and would pay off principle much faster aren't factored in. The ability to pay 25% as an interest-free down payment also doesn't factor in. If you, today, could buy a house for 3x your income with very high interest or one for 5x your income with medium interest for an equal monthly payment you'd choose the first option without blinking.