Like the right amount of oil, commercial mortgage–backed securities lubricate the commercial real estate engine, helping capital push back and forth by allowing lenders to extend credit on assets that traditional whole loan lenders, such as life insurance companies and pension funds, will not. Without it, class B and C assets and assets in secondary markets would all struggle to get a decent loan.

But in 2007 the engine flooded.

To reach the more than $220 billion in new CMBS issuance seen that year, lending fundamentals had to be watered down, resulting in overly aggressive underwriting, as well as a record number of interest-only loans. Those interest-only mortgages accounted for 85 percent of CMBS transactions that year, according to Standard & Poor’s ratings and Trepp data. The rest is history. The bloated market collapsed on itself, and the industry was left to ponder this question: Was it the driver or the vehicle that caused the crash?