[Aromasin]

This is only going off of what I've read from private interviews with Tesla employees (I'm sure there are some lurking on HN that can give a better idea), but it seems the production hell came mostly from the constant product updates that were rolling through. A connector on a wire harness becomes obsolete, and all of a sudden your camera that picks out that connector from a bucket needs updating, the arm that grips it needs changing, the milling machine that machines the hole for the connector needs changing etc. One up-issue knocks on to the entire production process. This isn't an issue with humans. You tell them the new part they need to use and that's it.