All of this material (or at least the true points) should be known by anyone in the fields of finance or economics. This is simply the way the world works. It's not a secret, it's just something most people don't know. Under the so-called Basel rules, banks are required to hold $8 in capital for every $100 in ordinary consumer and business loans. (Capital is a buffer against losses.) But residential mortgages were considered sufficiently safe to justify a requirement half that — $4 per $100 loaned. These rules remain in effect.