I graduated a couple years ago from Iowa State with an Industrial Engineering degree. Totally agree on how little most people understand on production issues. There's so much that goes into setting up a high volume assembly operation. To name a few:

* Bottlenecks are always being addressed. If you spend your time anywhere but the bottleneck operation, you're not increasing the capacity of the line.

* Quality issues can call back thousands of units and kill production for an afternoon. Hopefully the quality department catches everything, but without 100% testing they will be missing things. 100% testing of everything would drive costs up an insane amount, so sampling is done. Bad product slips through sometimes.

* The labor resources need to be effectively split so everyone is doing their task for the same period of time on the assembly line (and sub-assembly lines).

* Workers need to be trained and qualified for the positions they're doing. It could be as easy as 5 minutes of training on the new job content or as much as sending people to a training program because you can't hire the labor trained already.

* Fork truck drivers running into things can shut down an area during the accident investigation, preventing the typical restocking path (which is also finely timed out). Fork trucks run into things way more than most people would guess.

* Some production equipment breaks requiring unscheduled downtime. If you have redundant systems, you need to prioritize which units get processed next. You're already almost guaranteed to shut down production if you're running a lean operation.

* A supplier misses a delivery deadline. Especially on large assemblies like a car, you can't easily do more assembly and then add the part later. There's an order everything has to be assembled in. Yeah, you get to charge the supplier a shutdown rate, but that won't make your customer happy.

> This is a common challenge in lean manufacturing. Holding inventory is expensive in many ways, but having 0 on-hand inventory means every minor production hiccup is felt. Finding a balance to make supply chain, production, and management happy is a challenge.

* The sales people sold a product or feature which doesn't currently exist, so between design and production you've got to figure it out. Suddenly the line which was going to be streamlined with minimal product variety has 35 possible combinations rather than 4 and you have more logistics to deal with.

* A supplier abruptly stops supplying one of the products you are purchasing from them. You have 1 month to figure out a solution, send the trial runs through quality, write the work standards, etc.

* Procurement requests that a slightly different part is used from a supplier because it will save 5 cents/unit. Over 1,000,000 units that's $50,000 in savings. Do that on 15 parts in a big assembly and you're saving real money.

* The marketing campaign was more effective than anticipated, and demand for the next 3 months rose 25% (rather than the 10% boost anticipated). You now have to bump the production rate up an extra 15% which changes all the work instructions and line balancing, redo some workcells to allow for the increase in labor, increase traffic and congestion with the material handlers, buy/lease another fork truck, etc. There's a cascading effect. There's software which helps with the line balancing and possibly some of the internal material handling, but there's still some manual sanity checking of it all.

* The business is doing an IT transformation which can require anything from new/more computer systems on the line to completely retraining all of the staff on how to enter orders and production tracking into the system. Mentioning an ongoing Oracle installation will elicit condolences and heightened blood pressure from anyone who has been involved in one previously. I've seen Oracle implementations literally cause production employees of 20+ years walk off the job.

* The facility you're working in is land locked with no neighbor being willing to sell you land. Over 50+ years production lines were added, reconfigured, and removed. Shutting production down for 30 days to redo "everything" will cost tens to hundreds of millions of dollars and is only considered every decade or two.

That's a generalized list of issues I've seen while full time and on internships in a variety of industries.