> so I can simply re-run what didn't go through once it's back up, correct?

How would you know to do so?

> Say we wanted to sequentially save 3 items in our database table called numbers: [1, 2, 3] And we have a client that queries the table numbers for what was last saved, and will resume from where it left off.

So it saves all three.  It queries the database and sees all three.  Then it says "OK, I'm good" and exits.  But then the database crashes, and when it comes back up only the 1st one is there.  Unless the client is always periodically rechecking, it won't know anything has been lost in order to fix it.