In examples like the one just cited, we assume that the situation is not altered essentially by any unmentioned extraordinary factors. Conceivably, for instance, a professional actor might objectively need a cigarette in order to realize a character who was a smoker. Furthermore, cigarettes can have exchange-value (discussed in Section 4). Historically, they have sometimes served as a common medium of exchange following the collapse of a currency during a war or other calamity. In such extreme circumstances, cigarettes may become vital to the survival of smokers and nonsmokers alike. In applying "need" and other complex concepts objectively, it is necessary to take all such contextual factors into account.

Not only do we sometimes desire things we do not need, but we may need things we do not desire. For example, a person may be loath to embark on an appropriate program of physical exercise, even though the latter is vital to his or her life, health, and well-being. Like other emotions (see p. 1.3:86), however, desires can be modified over time by one's conscious thought processes. Consequently, people who consciously adopt a positive, life-oriented outlook often find that their desires become increasingly in tune with their needs.

Physical exercise is vital to one's life, health, and well-being.

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