The whole Greek culture was permeated with a competitive spirit. It was a part of the education: young Greeks were encouraged to be the best, always and everywhere, and to outdo all the others. This ideal is already present in the Iliad, the book that formed the basis of the education of the whole Greek elite. Winning a contest led to fame.
What did they know?
Munro and Macan note Herodotus giving the names of six major commanders and 29 myriarchs (leaders of a baivabaram, the basic unit of the Persian infantry, which numbered about 10,000-strong); this would give a land force of roughly 300,000 men. Other proponents of larger numbers suggest figures from 250,000 to 700,000. One historian, Kampouris, even accepts as realistic Herodotus’ 1,700,000 for the infantry plus 80,000 cavalry (including support) for various reasons including the size of the area from which the army was drafted (from modern-day Libya to Pakistan), the ratios of land troops to fleet troops, of infantry to cavalry and Persian troops to Greek troops.