Subprime borrowers are people who probably have pretty poor credit ratings. They may have a history of bad financial management, perhaps including collection accounts, repossessions, maybe even a bankruptcy. At any rate, they are perceived to be more likely than the average borrower to default on this loan. A subprime lender exists to lend money to borrowers who are not expected to act responsibly in the repayment of the debt. The interest rate that a subprime lender charges will be higher than usual because of that increased risk of default. Subprime lenders know about the risk; they fully understand that these borrowers cannot really be counted on to repay their debt. Why should they be surprised when it turns out exactly the way they expect it to?

Lending takes place when one business or individual lets out money to another business or individual, for a defined period of time, and at a specified rate of interest. When you're talking about a mortgage, it might be – for example – a fixed-rate loan for 30 years, at 5.7% interest. (The annual percentage rate is referred to as the APR.) This is a common type of mortgage: the borrower agrees to pay the lender back over a period of 30 years, at a yearly 5.7% interest rate.

So there are three elements of the puzzle: borrowing, subprime, and lending. What else has contributed to the current situation? Lending practices of dubious quality joined with a huge number of subprime borrowers whose ability to repay their loans was questionable. Yes, we are definitely in a mortgage crisis; foreclosures have never been higher. Whose fault is that?

When a homeowner falls behind in monthly payments on a mortgage, the bank takes notice. If payments are not made for three months, generally the process of foreclosure is initiated. This is a lengthy and costly process that often spans many months. The home is foreclosed and the property is repossessed by the bank.

Actually, the bank would prefer the borrower to repay the debt rather than have to take the property. A bank is not a real estate company. There is also the risk of censure from the federal government if too many of their loans are defaulted upon. For these reasons, foreclosures can take a very long time. The bank is in no hurry.

The majority of subprime mortgages are nowhere near as easy to understand as the example we gave above. Lenders have gotten more and more creative in the last few years, in an effort to attract more subprime borrowers. Many of these borrowers are now carrying an adjustable rate mortgage (ARM). The initial low interest rate of these loans allowed lots of people to get involved in a loan for which they might not have qualified otherwise. When the loan resets in about two years, the interest rate usually goes up considerably. In addition, some of these loans have prohibited refinancing in the first several years.

Borrowers, subprime mortgages, lending, and foreclosure have all worked together to give us this picture. Contributing in addition were falling house prices, rising mortgage payments, changing real estate markets across the country, difficulty of finding accessible mortgages, and a glut of houses for sale on a market where few people are buying. Here's the completed puzzle: the mortgage mess.