Why were runs during the financial crisis of 2007-2009 not limited to institutions with large exposures to subprime mortgage lending? All banks and shadow banks had large exposures to subprime mortgage lending and so were directly affected by the problems in that market. Shadow banks that did not have large exposures to subprime mortgage lending were largely unaffected by the crisis. Banks and shadow banks are highly interconnected with one another and so problems in one institution can quickly spread to others, making otherwise healthy institutions vulnerable. When one bank fails, other banks must follow, and so the failure of one bank results in large and cumbersome fines paid by similar institutions