In the made-up town of Brickton, prices kept rising, so families borrowed to buy houses, paying the loan back a little at a time.
Ana the lender bundled many loans into one parcel and sold it to Cy, so she had coins to lend again. The parcels passed along a long chain.
Then house prices fell, some families could not repay, and nobody knew which parcels held the shaky loans. Everyone doubted every parcel, and lending froze.
This happened for real in 2008. Many things played a part, and many people lost jobs. Afterwards, new rules asked lenders to check borrowers and keep more coins in reserve.