Pompey
Pompey fought Caesar at the Battle of Dyrrhachium (48 BC), in which Caesar lost 1000 men and Pompey lost 2000. Because he failed to pursue at the moment of Caesar's defeat, Pompey threw away the chance to destroy Caesar's much smaller army. As Caesar himself said, "Today the enemy would have won, if they had a commander who was a winner" (Plutarch, 65).