Discipline

RESOURCE: DISCIPLINE

Hatred and Discipline are the Demon Hunter's two Skill Resources in Diablo 3. Discipline is the blue colored resource on the right side of the Demon Hunter's resource orb. The Demon Hunter will need Discipline to perform Discipline Skills. Discipline will regenerate slowly, but can also be instantly replenished by using Preparation.

Also See:

Discipline

Generate Extra Discipline
Reduce Discipline Costs
Discipline Regeneration
Maximum Discipline 

Demon hunters are perpetually at war with themselves. They hold no hope for a return to their former lives, but they fight and stalk demons with a passion. Those hunters who live to train others become deliberate and cautious and, yet, their impulses scream to meet demonic violence with more violence.

Every arrow that demon hunters launch is dipped in spite; nearly all of their attacks are delivered with Hatred, a cold, righteous anger that renders them utterly merciless to their enemies. Their Hatred is nearly endless; it recovers quickly, as, even at rest, demon hunters are filled with the desire for vengeance.

Those hunters who would hope to make any sort of true impact must temper their Hatred with a second resource: Discipline, the caution and care that ensures they live to kill another day.

Discipline is precious to demon hunters. Not only does it return slowly, requiring more reflection and patience than their Hatred-based attacks, but they must rely on it for every defensive maneuver – trapping enemies in place, vaulting out of the way of teeth and claws, and dodging hails of spines and arrows.

It is a simple matter for demon hunters to stand in place, icy with Hatred, and send a volley of projectiles at the hordes of their enemies. But, when they fail to defend themselves with Discipline, hunters leave themselves able to be slaughtered. A careful balance of Discipline and Hatred is the most likely way hunters ensure their survival.