To think good thoughts requires effort. This is one of the things that discipline – training – is about.
In its natural sense, discipline is systematic instruction intended to train a person, sometimes literally called a disciple, in a craft, trade or other activity, or to follow a particular code of conduct or "order". Often, the phrase "to discipline" carries a negative connotation. This is because enforcement of order–that is, ensuring instructions are carried out–is often regulated through punishment.
Discipline is the assertion of willpower over more base desires, and is usually understood to be synonymous with self control. Self-discipline is to some extent a substitute for motivation, when one uses reason to determine the best course of action that opposes one's desires. Virtuous behavior is when one's motivations are aligned with one's reasoned aims: to do what one knows is best and to do it gladly. Continent behavior, on the other hand, is when one does what one knows is best, but must do it by opposing one's motivations. Moving from continent to virtuous behavior requires training and some self-discipline.
The regulation of the behaviors of members of any military, involving rules that govern goal orientation and behavior inside and outside the institution, including the socialization processes that happen in military training. Rules of discipline are firmer or laxer depending on the prevalent culture of the military's country or institution. As early as the time of the Roman Army, discipline was enforced through military justice, but broader compilations of laws such as the Codex Theodosianus contained provisions dealing with military discipline.