[gorjusborg]

The core innovation of 'double entry' is that you can see the flow of money between accounts for every transaction.

This is possible because you (the accountant) are always adding a back-reference from the other account (hence the 'double' in 'double entry').

There's really not much to it. It throws people that are new to it for a loop, I think, because it is a strange way of behaving, and it isn't obvious why you're doing it until you have to track down something that doesn't balance. It's just a disciplined behavior that accountants started using because it allows one to track things that were difficult without it.