The system is self-limiting because at some point, a very aggressive lender will overshoot, and lend at a rate at which they are not profitable.

FORBES

Whether or not Gordon Brown's Treasury had an excessively optimistic view of the budget deficit, he certainly severely underestimated the degree to which Her Majesty's Government would be on the hook if Britain's world-beating financial system got into trouble: The financial sector bailouts account for eight percentage points of the overshoot in our debt.

BBC: Debt and the crisis: How did governments get it so wrong?