For a fictional point of reference to the above sentiment: remember HAL 9000 in 2001: a Space Odyssey, and the explanation of why it went homicidal as given in

For a fictional point of reference to the above sentiment: remember HAL 9000 in 2001: a Space Odyssey, and the explanation of why it went homicidal as given in 2010: Odyssey Two. It had two directives: preserving human life and the mission; the first conflicted with its ability to ensure the other's success once the humans started plotting to turn HAL off. In the movie (at least), it was implied that the mission's importance was imparted by Presidential authority, and was given a higher priority than anything else.