"In philosophy, the best motivation lies in aporia." 

Aporia: to be at a loss, without a path to follow. (Webster's) 

For the Athenians, the nomadic Scythians were aporoi. While the Athenians valued authochthonous birth, the Scythians had absolutely no attachment to any place and were always somewhere else. For the imagination of urban Greeks, nomadism was the indelible mark of the Scythians' distance from civility, the sign and substance of an alien existence, the quintessence of otherness. (see also war machine

(from Steven Greenblatt, Marvelous Posessions, in reference to Francois Hartog, The Mirror of Herodotus: The Representation of the Other in the Writing of History.)