The Athenian general Demosthenes, who fought in the Peleponnesian war, used surprise in all his military operations. Chiefly because of this reason he has sometimes been labeled as an original thinker, if not a misunderstood genius. This study asks whether Demosthenes deserved the accolades that have charaterized much of the modern studies of the general and his age. The investigation identifies what factors were responsible for Demosthenes' successes and failures, and draws attention to the hitherto unnoticed contributors to the general's victories. The study points to Demosthenes' inclination to take great risks, his uncompromising belief in the effectiveness of surprise in war, and his readiness to ignore objective difficulties in pursuing his goals. In addition, Demosthenes' campaigns indicate a narrow perception of military problems, a tendency to give up rather easily when things were not going according to plan and an inability to lead an orderly retreat.