The airplane with a pilot on board has a demonstrated and theoretical performance envelope. This is physics combined with psychology. The impact of a human being's involvement exists at the crossroads which separate demonstration from reality. To be more specific, a human's reaction to the same event will be markedly different depending on who or what initiates the event. Surprise, for our purposes, may be loosely defined as the occurrence or initiation of a random event that occurs without warning.
Surprise is a factor that is most desirable and almost impossible to achieve in simulation.
However, the effect of surprise can be easily demonstrated. Hold a one dollar bill with one hand by the short edge, so that it is longest from top to bottom. Now, release the bill with your upper hand and try to catch it with your lower hand. Now have somebody else drop the bill for you. You will probably find that your reaction time is significantly longer if you're not prepared for the bill to drop.