Or just this one scene. It kinda ties the whole theme together.

Basically, Lewis Ranieri's mortgage bonds were amazingly profitable for the big banks. They made billions and billions on their 2% fee they got for selling each of these bonds. But then, they started running out of mortgages to put in them. After all, there are only so many homes and so many people with good enough jobs to buy them, right? So, the banks started filling these bonds with riskier and riskier mortgages. That way, they can keep that profit machine churning, alright? By the way, these risky mortgages are called "subprime." So, whenever you hear the word "subprime," think "shit."