Bank errors in your favour do happen, or at least they did - one happened to me maybe twenty five years ago. I was broke and went to the bank to pay in my last £30-something of cash to cover an outgoing bill. Stopped at the cash machine outside my bank to check my balance was sufficient now, and found that the cashier had put an extra 4 zeros on the figure I'd deposited. I was rich! I was also in my early 20s and not thinking too clearly I guess because my immediate response was to rush home to get my passport with the intention of going abroad and opening an account into which to transfer the funds, never coming back. I checked my balance again at another machine closer to home and the bank had already caught and corrected their mistake. Took them maybe thirty minutes.

After a bit of occurred to me that I was lucky really, because I didn't know what the fuck I was doing and the funds would have been traced very easily and I'd have been in deep shit.

But yeah, anecdotal, but shit like that did happen. I assume it's more rare these days as fewer humans are involved in the system, and fewer people use cash.