a) There was not enough fertile land for ordinary Greeks.
b) There was not enough food.
c) The desire of ordinary Greeks to avoid a military clash between the demos and the nobility.
Since Greece had few soil suitable for agriculture, there was not enough food, a struggle was waged between the demos and the nobility: all this forced the Greeks to develop new lands – colonies. The most famous of them on the Black Sea coast are Olbia, Chersonesos, on the Mediterranean coast – Syracuse, Carthage.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.