SET or SCT believes that the two key determinants of behavior are perceived self-efficacy and outcome expectancies. In other words, the extent to which the person feels able to actualize / implement behavior, and the consequences (both negative and positive) of performing the behavior. SCT is actually an extension of SET in that it maintains that the environmental factors as well as human factors are all intertwined in determining self-efficacy; in fact that the three concepts play one inseparable whole in determining health conduct and response to prevention or to reaction of disease. The three main factors that induce a person to change his health behavior are the following: (i) self-efficacy, (ii) goals, and (iii) outcome expectations.

Individuals who have a powerful sense of self-efficacy can change health behaviors even when impeded. It is this very sense of empowerment -- of feeling ability to act and to change matters -- that propels them past inertia and causes them to persist despite challenges. The adoption of new behavior, in turn, causes changes...

Sociology, for instance, believes that the environment is a product of the person. SCT, integrating cognitive, emotional, and behavioral aspects, asserts a fusion of cognition, behavior, and environment whereby, through individual changes, a person can change his environment that, in turn, affects his behavior.
Examples where SCT can be used effectively are pain control where via distraction, for instance, a person can transcend pain. SCT can also be used to overcome stress through stress-relieving methods such as medication or yoga.

Sources

Sutton, S. (2002) Health behavior: Psychosocial theories. Retrieved on 1/13/2011from http://userpage.fu-berlin.de/~schuez/folien/Sutton.pdf

National Cancer Institute. (2005). Theory at a glance: A guide for health promotion practice. U.S. Department of Health and Human Services.

Weiten, W. (2007). Psychology: Themes and variations. USA: Thomson-Wadsworth.