@JPB,
Total Meltdown:
My employees got paid today. They went to the bank across the street and cashed their checks, taking money out of that bank. That left that bank, for a time, a bit short of cash. No problem in normal times. They could borrow the money from another bank for a few minutes, literally for a few minutes, until the grocery store across Main Street came in and made their deposit.
Add a whole bunch of zeros and you have, in the U.S. and the world, trillions of dollars, yen, euros , pounds and yuan moving amongst banks. Sloshing around.
But what happens if one of those banks, in New York, London, Paris or Hong Kong, is perceived to be on the brink of failure - within minutes or hours or perhaps, in the long term, a day? Inter-bank lending stops.
The system seizes up, like a car engine with peanut butter mixed with the oil. Lending between banks, like the car engine, stops, with catastrophic results.
That is what almost happened, I think, near the end of the Bush administration and the start of Obama's. I am sticking with that scenario.