On the four things that we wanted to ensure were covered on human fatigue, the principles are as follows: that human fatigue is governed by physiology; that human alertness is affected by circadian rhythms; that human performance degrades in relation to hours of wakefulness and accumulated sleep debt; and that humans have baseline minimum physiological sleep needs. Those are important things that people have been asking to have recognized.
On April 23rd, 2015. See this statement in context.