How are lower class citizens predestined to enjoy their jobs?

The Centre conditions all the non-Alpha and Beta embryos for their future status in society by dividing them into Gammas, Deltas, and Epsilons. Thus, the Alphas represent the intellectually superior group, followed by the Betas, and continuing down to the Epsilons, who have little to no intelligence. "Identity" comes from the Conditioning Centre through the selection of the embryos into each of five groups. "Stability" occurs through the limitations placed on the intelligence of each group. Limiting the intelligence of each person to fit their future job is one way this society makes them happy.