The catch is here:
if you have $100 and reserve requirement is 10% then you can lend $90
then, if the $90 that was lent is deposited back in your bank, you can lend $81 more (etc. but two levels is enough for this example).
that's how $100 initial deposit turned into $90+$81=$171
but the total amount of deposits is $100+$90=$190. If bank loses those $171, how is it going to repay the $190 when demanded?