Why does running the production line overwhelm me?

Running the line overwhelms you, and that is understandable. A line is many things happening at once, all depending on each other, and any one of them can go wrong while you are watching another. Holding all of it feels like too much because, held all at once, it is. The overwhelm eases when you stop trying to watch everything equally. Not every part of the line matters the same. There are a few points where trouble spreads fastest, and there are the rest. The skill is not seeing it all. It is knowing the few places to watch closely and letting the rest run. Find the one or two spots where problems hurt the most or happen the most, and put your attention there. Let the steadier parts take care of themselves for now. You cannot hold the whole line in your hands at once, but you can keep your eyes on the places that count, and that is what running it well actually looks like.