In this article, the author considers the need for changing health behavior in youth. The author begins by discussing how people learn health behavior which could help educators in understanding the reasons why it is often difficult to effect changes--and how educators may succeed. If the aim of health educators is to change behavior, the author suggests that their focus must be on the "application" of health knowledge. This requires that they deal with two important issues: (1) the guiding principle underlying "all" desirable health behavior; and (2) possible problems and difficulties in applying health knowledge to everyday situations.