Difficult to test. What if some workers are chronicly sleep deprived and that contribution was the tipping point for some of them, but not all sleep deprived wo

Difficult to test. What if some workers are chronicly sleep deprived and that contribution was the tipping point for some of them, but not all sleep deprived workers? What if some workers are chronicly anxious, causing sustained elevated stress hormones that combined with other factors put them over the tipping point? So many possible confounding variables