As individuals are involved in self-quantification, increasing fields are applying self-quantification with technical support, and a clear understanding of the influencing mechanism and effect boundary of self-quantification is indispensable. Focusing on the field of physical fitness, under different goal settings, the influencing mechanisms of self-quantification on an individual’s participation performance (outcome, experience, persistence intention) and behavioral decision-making (category selection, novelty-seeking) are analyzed and confirmed. The results show that when there is no goal, self-quantification will enhance outcome salience, thus enhancing the individual’s participation outcome and selection for highly healthy categories; self-quantification will reduce perceived enjoyment, thus damaging participation experience and novelty-seeking, but does not affect the persistence intention. When there is a goal, self-quantification will enhance perceived certainty, thus reducing the individual’s participation outcome and selection for highly healthy categories; self-quantification will enhance perceived enjoyment, thus improving the participation experience, persistence intention, and novelty-seeking. Compared to descriptive analysis of phenomena, through laboratory and field experiments, this research confirms the influencing mechanism and effect boundary of self-quantification on an individual’s activity participation performance in real situations. This provides a theoretical basis for understanding the targeted behavioral decision-making patterns of individuals in different types of self-quantification activities.