What will trigger the next recession?

[Doug Utberg]

Background: The economy is on a tear, but trees don't grow to the sky.  At some point, it will over-extend and go into recession when financial commitments default.

Last time, the trigger was a default on home mortgages.

It doesn't look like that is a major risk area currently.  However, there is going to be something.

My theory - I think that commercial debt from companies in the retail sector is a major weak point for the economy.  When the financially troubled big box retailers start defaulting on their debt service payments, I see the potential for a causal chain that spreads out to the broader economy.  (Not nearly as severe as 2008, but will definitely result in lots of vacant commercial property and much higher risk premiums for bank lending)

What do you think it will be?