Could someone explain something fundamental to me about the need for double-entry accounting? Why can't your source of truth instead be proper SQL tables following these schemas (using Python tuple/list notation for convenience)?

  transactions: [
    (txID, timestamp, [
      (accountID, delta, otherInfo),
      ...
    ], reason),
    ...
  ]

  accounts: [
    (accountID, routingNumber, accountNumber, ownerID),
    ...
  ]

Crucially, notice that "accounts" don't track balances here, and so I'm asking: why would I need TWO entries per transaction, and why would I need to do my own tracking of the balance of every account, when I can just keep a single entry per transaction in a proper ACID database and then build any view I need on top (such as running balances) with a battle-tested projection mechanism (like a SQL View) so that I still track a single source of truth?

> It’s just that…it goes without saying that fintech companies should know better

haha, if only.

move fast, break everything if it gives profit

> And yet, I used to work for a startup that, on every transaction, simply lost track of a couple of cents. As if they fell from our pockets every time we pulled out our wallets.

is this not the literal plot of Office Space? did you check for a Michael Bolton employee?