Earlier quoted context omitted.
> Why not just hold them > If there is a run If there is a run, they become forced sellers, because they don't have enough cash on hand to meet withdrawals. That's the whole story. They must prevent a bank run.
Can’t they just not honor the run, so that they can honor it in the long term, rather than selling at a loss and not being able to honor 20% of them?
You lend out on shorter terms than you figure your depositor will need and pray they don't need it back. If they all do though, you're screwed.
It's statistical multiplexing as applied to piles of other people's money.