BrainWorms

And if you rush them, then things go wrong in a hurry. It doesn't matter how much documentation you have if the operator skips steps or plain old makes a mistake.

I've personally blown up thousands of dollars in tooling making stupid mistakes when I was a junior machinist being told we had deadlines to meet. I've seen other guys forget to probe a work offset and crash the machine so badly it needs a spindle rebuild. A press operator can wreck a $100,000 die set if they make even relatively easy mistakes, and if that happens to the wrong tool, it can completely shut down production for months for a repair or rebuild.

If there's a 1 in a million chance that any of those 10,000 employees makes a big, showstopping mistake on a given day, then after 100 days, there's a 63% chance of that event happening.