The crypto model of single entries with "from" and "to" field works well for transactions. For example you move $100 from checking to savings account, something like the following will capture it perfectly.
```json { "from": "Checking", "to": "Savings", "amount": 100 } ```
This is basically what a crypto ledger does.
But the main reason why we need double entry accounting is that not all accounting entries are transfers. For example, is we are logging a sales, cash increases by $100, and revenue increases by $100. What's the "from" here? Revenue isn't an account where account is taken from, it is the "source" of the cash increase. So something like the following doesn't capture the true semantics of the transaction.
```json { "from": "Revenue", "to": "Cash", "amount": 100 } ```
Instead, in accounting, the above transaction is captured as the following.
```json { "transaction": "Sale", "entries": [ { "account": "Cash", "debit": 100, "credit": null }, { "account": "Revenue", "debit": null, "credit": 100 } ] } ```
It gets worse with other entries like:
- Depreciation: Nothing moves. You're recognizing that a truck is worth less than before and that this consumed value is an expense. - Accruals: Recording revenue you earned but haven't been paid for yet. No cash moved anywhere.
The limitation of ledgers with "from" and "to" is that it assumes conservation of value (something moves from A to B). But accounting tracks value creation, destruction, and transformation, not just movement. Double-entry handles these without forcing a transfer metaphor onto non-transfer events.