American banks seem unable or unwilling to follow the simple algorithm &quot;process the transaction immediately, if the sender does not have enough money to complete it, decline it.&quot;<p>Instead we depend on forms of payment which have latency measured in days (checks, direct deposit) and we process debit card transactions on a delay of hours to days. If you are playing close to $0 it&#x27;s very easy to make a mistake and then fall below $0. The bank has effectively trusted you not to do this, and you did it, so they charge you a fee as punishment. Except you have less than $0, you can&#x27;t pay the fee.<p>If you do this, then your bank might close your account and put you on the ChexSystems blacklist, which will prevent you from getting any new accounts for a few years.<p>AFAIK ChexSystems blacklisting is pretty much the only reason to be unbanked (except by choice as a form of protest, I guess?) Simply doing proper OLTP would eliminate the weird artifact that is overdraft and entirely sidestep the problem of unbanked people.