Agricultural growing, fishery & livestock, mining, all of these productions are associating with climate & weather, and availability of natural resources after many years of exploitation if it still can be enduring. The fates of these participants would be direct connected with what natural environment rather than they can control by their own.
Manufacturing sector would demand manpower of low educated labors, however, technologic advancement; automation by great leap in manufacturing brings down the worth of physical manpower for this sector --the Secondary sector
The tertiary sector requires higher educated workers serving for people rather than materials and machines in the primary and secondary sector. New generation who now has received higher education is reluctant to join the both sectors which are considered low quality of work life. They would prefer to dedicate their mentality for better income rather than physical power exhaustion