Here’s the thing. I have $20 in my pocket. My friend calls me up and ask to borrow $20. I am OK with that. So what do they have to do. They now must come to meet me, and take my $20 bill. They then will use that money as they need to, or return home. This costs time and resources. If everyone has an electronic account from the same bank, and using the same system – I can simply transfer $20 from my account into their account before they can even get a jacket on to meet me. When my friend is able to pay me back, they will simply send money from their account to my account. And since the account numbers is based off of the NIIN, the only thing needed to know is NIN numbers which are designed to be public knowledge.