When I am woring on knowledge representation and reasoning, I keep asking myself a question: Why do we need automated reasoning systems?
I believe this is a strong enough case: 2009 Air France Flight 447, crashing into the Atlantic due to pilots' errors.
More details can be found at http://www.usatoday.com/NEWS/usaedition/2011-05-31-AirFrance31_ST_U.htm
Human beings have many volunable "features." We panic when unfamiliar emergency happens. And this causes our brain no longer rational. Therefore, we need a rational assistant for that kinda cases.