Sociologists describe the pattern of selection in heterogeneous returns to college education as negative, in contrast to the positive selection proposed by economists. This article moves beyond such a conflicting contrast, suggesting that the contradictions between "selection on observables" and "selection on unobservables" are at the heart of the contradictions between these two selection hypotheses. Employing both sociological and econometric counterfactual approaches to estimate college treatment effects, this article shows that the negative pattern of social selection based on family background characteristics and the positive pattern of self-selection based on the principle of comparative advantage are not mutually exclusive-both patterns emerged in the early 1990s, when Taiwan's higher education systems were rationed with structural barriers. Since Taiwan's swift expansion in higher education over the last two decades, nevertheless, there have emerged signs of decline in the treatment effect for the treated, coupled with a sorting loss in the face of negative social selection.