I've spent a few weeks on one, so not zero, but not a lot.

Note that I simplified greatly a real assembly line, and there are lots of different lines with different configurations. Nearly everything is multiple lines. There are often buffers along the way so that you can get ahead of the line by a little (or if you need to use the restroom the line continues). Sometimes there are two people in a station with the understanding that if both are perfect they are 80-90% busy (or some such number), but if someone is slow the other can help up. Lines often go slower than possible because of safety. There are likely more issues, but there is a point where the line is waiting on the slow person.

With the above in mind, what am I missing?