I wrote this a long time ago. It does tend to upset some people, but it did work as an accurate and testable mental model:
https://django-hordak.readthedocs.io/en/latest/accounting-fo...
https://django-hordak.readthedocs.io/en/latest/accounting-fo...
A way I learned about it was that you want to be able to know the tangible cash value of your business at any given moment.