Thank you. IMO a couple of good motivating examples (as I said a couple of years ago: https://news.ycombinator.com/item?id=32497843 https://news.ycombinator.com

Thank you. IMO a couple of good motivating examples (as I said a couple of years ago: https://news.ycombinator.com/item?id=32497843 https://news.ycombinator.com/item?id=32497843) are: • Bank accounts and cash. If you're tracking a single number, do you track a cash withdrawal (and then ignore purchases with cash), or do you ignore cash withdrawals (and track cash purchases)? With double-entry accounting, you just track withdrawals as money flowing (Bank account) -> (Cash), and purchases as (Cash) -> (Stuff) or whatever you want to call it; both are equally cleanly represented. • Bank accounts and credit-card (or other loan) repayments. Similar thing: if you were to use a single number, do you change it when you make a purchase with a credit card (and ignore tracking paying your credit card bill) or do you change it when you pay your credit card bill (and ignore purchases with your card)? With double-entry accounting you just treat them as money flowing (Bank account) -> (Credit card) and (Credit card) -> (Expenses). And your bank account statements and credit card statements will both make sense in isolation, if you have this complete picture. (Personally I found https://beancount.github.io/docs/the_double_entry_counting_method.html#introduction https://beancount.github.io/docs/the_double_entry_counting_m... even more useful for the basic idea than https://martin.kleppmann.com/2011/03/07/accounting-for-computer-scientists.html https://martin.kleppmann.com/2011/03/07/accounting-for-compu... but both are interesting.)