You could borrow against a house in '08 or against tulips in 1634. If it's the rising side of the market, you'll make a killing doing this. If it's the oppos

You could borrow against a house in '08 or against tulips in 1634. If it's the rising side of the market, you'll make a killing doing this. If it's the opposite side, then your collateral will vanish. Whether vanishing collateral matters to you depends a great deal on the nature of the debt you took out and what you spent the loan on.