One secret of brave Spartans

Have you ever wondered why Spartans were able to spend so much time of the lives on military exercises? I guess, everyone watched the movie about 300 brave Spartans and their king Leonidas who did not let Persian king to invade ancient Greece. Everyday life of Spartans was shown in great details omitting one "dirty" secret. The helots. 

Spartans were one a very few ancient Greek nations who had their own slaves of the same Dorian origin. In other words, these slaves were their Greek fellows by birth, mostly from Messenia. This was quite unusual for the rest of Greece, where slaves were mostly foreigners, who were captures during wars.

The helots outnumbered Spartans many times by its population. They either worked on Spartans lands or were carrying all domestic work. Yet Spartans hated them as much as anybody could hate his worst enemy. This unusual hatred of the Spartans towards the helots originates in fear. Given the relatively small number of Spartans in comparison with huge slave population, they feared that helots would attempt to destroy them.

This fear contributed to mistreatment of helots. Because of it, Spartan men always carried their spears, undid the straps of their bucklers only at home. That may also explain why there were so inclined to succeed in military training.