Feed is related to Hunger. Hunger would make you want to Buy. you would Buy because Better. 
Ambition is a type of Drive. Ambitious is etymologically related to Ambition. 
Feed <--RelatedTo--> Hunger --CausesDesire--> Buy --MotivatedByGoal--> Better 
Drive <--IsA-- Ambition <--EtymologicallyRelatedTo-- Ambitious 