Margin call typically happens in context of falling stock market: more investors find themselves at the margin, margin calls create more margin calls. Being frightened of cholera is not going to give you cholera, but being frightened of a financial crisis can bring on one. Trust underlies the entire financial system: currency crises. Value of money quickly decreases over week, days, hours. First financial panic that seems to interest scholars: the kipper-und wipperzeit: coins have milled edge stop from theft. Clipping: shave a bit off edge of coin and end up with shavings you can reuse, coins were misshapen. Debasing coins: take precious metal and mix with cheaper metal to make more coins, overtime can become more debased, undermines faith in currency system. Different currencies in milan had to trust retailer that the change was worth the right amount. No guarantee of currency for hundreds of years.