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 the case because enforcement of order is often regulated through the threat of punishment to ensure given instructions are carried out.
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 can be described as 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.