The denial letter arrived saying that the reason was insufficient value or type of collateral.

For example, the leak of credit card information at Home Depot in 2014 was due to insufficient PCI DSS compliance.

Also, they can have their ACH transfer bounce, like has happened to me in the past for insufficient funds in their checking.

On SF deals I originated default was about 3 to 8% off hand, usually due to insufficient down payments and buyers just changing their minds.Anyway, the issue is lack of down payments and slow appreciation that puts a buyer in a 3/4 year deal at a point where they see little reason to go through the efforts to sell on their own.

Distilled down to a single essence: people are insufficiently employed.

If insufficient, you'll need to go thru the shirt sale process. 

(No Enron, Worldcom, Healthsouth, Bernie Madoffs, etc, etc, etc, etc, in my past.)Finally, The “best and brightest” in DC mess with simple concepts frequently to maximize taxes on those with insufficient resources to mount an effective lobbying effort...so for reasons they alone can fathom, something above may have been arbitrarily deemed illicit.

With use it or loose it budgets that are borderline sufficient/insufficient, something has to give.

I am a motivated baby boomer staring down the barrel of an insufficient retirement account. 

A Ponzi is slightly different, more of a "robbing Peter to pay Paul" scheme where money from new investors is used to pay returns to earlier investors in order to hide the fact that whatever the investment vehicle is that the scheme is based upon (originally the arbitrage of postage stamp coupons) is insufficient in realizing the promised returns.