Considering our experiences in everyday life, the result of research based on sample assumed to be derived from a “population” cannot afford individual predictions. That is because the variabilities within individuals which play an important role in actual psychological processes are erased from the data in samples-based studies. In this article, we begin the discussion with how the intra-individual variance contributes to individual prediction. As case study works on the basis of variability within each individual, it explores the intrinsic mechanism of development and emphasize the connection between person and environment. The question of how to generalize from case studies requires that the researcher to selectively consider some of the variance and construction of a hypothetical model that shows how different features of oppositions (Yin and Yang) are integrated into an abstract whole that is applicable to all individual cases.