Every journal entry usually triggers side-effects: SMS the user, email the merchant, fire a webhook to a partner, push a notification to your mobile app. Naive code does the SMS send right after the INSERT in the same function. This has three failure modes, the SMS goes out before the DB commits, the DB commits but the SMS fails, or the process crashes in between. The outbox pattern fixes all three by putting the side-effect intent INSIDE the same database transaction as the ledger entry. A separate worker reads pending outbox rows and sends. At-least-once delivery guaranteed. The journal entries below are simple deposits; the lesson is in the commentary about HOW to commit them safely alongside their side-effects.