To continue the analogy, it’s the difference of me texting you that I’m moving $20 of our shared balance back to your side of the books, which would take a few seconds, versus me hopping in the car and driving 10 minutes to your house. Well, on average it’s a 10 minute drive, but sometimes there’s a lot of traffic and it may take 30 minutes or an hour, or maybe I just took the scenic slow route because it was cheaper on tolls. Not to mention the added cost/fees associated with me having to make that drive.

To put it in bitcoin terms, a Lightning payment (us updating our shared balance/ledger) is nearly instant, versus an on chain transaction (me driving to your house to pay you in cash) which takes on average 10 minutes, but sometimes more or less depending on various factors.