IrnBru

Because that isn't a physical law.. it's a metric.

Of course I am being simplistic and a run can occur precisely because there is more than one bank...

But on the international transfer thing... you selling USD and buying EUR doesn't result in the creation or destruction of any USD or EUR deposits overall, unless the central bank/government is intervening.

That is irrational behaviour. Depositors should spread their cash across multiple banks. This is very basic risk management.

Not true. Imagine there was only ONE bank.

Borrowing short term and lending long is what all banks do. The problem here is a lack of diversification.