even computers makes mistakes (or more correctly: even optical scanners misread numbers)
two recent examples:
the bank deposited $3500 into my wife's account erroneously (the image of the deposit slip clearly was someone else's). It sat there for a week until she called them about it. they had to manually reverse it - the computer reconcile wasn't going to catch it.
last fall the electric company incorrectly credited my business account $13,000 (usual bill: $355). took them three months to figure out where the $13K belonged. (insert breaking bad joke here)
in both cases, I'm not sure they would have figured it out had we not called and told them the money wasn't ours...
