Goal is a widely used concept in requirements engineering methods. Several kinds of goals, such as achievement, maintenance and soft goals, have been defined in these methods. These methods also define heuristics for the identification of organizational goals that drive the requirements process. In this paper, we propose a set of principles that explain the nature of goal-oriented behavior. These principles are based on regulation mechanisms as defined in general systems thinking and cybernetics. We use these principles to analyze the existing definitions of these different kinds of goals and to propose more precise definitions. We establish the commonalities and differences between these kinds of goals, and propose extension for goal identification heuristics.