According to my opinion, I feel that this statement indicates about the presence of hidden causes for human error. This is because human error will not necessarily be generated when the human being is absolutely in a perfect state of physical or mental health. In other words, there can be human errors caused as a consequence of the unhealthy physical or mental conditions of a pilot or a co-pilot. An example of an unhealthy mental health condition of an aviation officer could be a sudden headache or a mild eye pain. An example of an unhealthy physical health condition of an aviation officer could be a feeling of nausea or fatigue while conducting aviation operations.