We investigate the effects of static stress transfer from the 1999 Chi-Chi Taiwan earthquake to the subsequent Chia-Yi earthquake by using Coulomb failure assumptions. Our results provide substantive evidence that changes in normal stress unclamped the Chia-Yi rupture surface but that changes in shear stress discouraged the Chia-Yi earthquake. Combining these two counter effects, we determine that the Chia-Yi earthquake could have been activated by the Chi-Chi earthquake provided that there was an increase in Coulomb failure stress of less than 0.2 bars on the grounds that a friction coefficient of 0.7 ≤ μ ≤ 0.75 and a Skempton’s coefficient of 0.75 ≤ β ≤ 0.85 are very feasible mechanical conditions. Equally important, we find a poor correlation between the changes in Coulomb failure stress from the Chi-Chi earthquake and the slip amplitudes of the Chia-Yi earthquake, which implies that fault heterogeneity could have very well reduced the effects of the changes in static stress caused by the Chi-Chi earthquake. Beyond this, the concentration of transient stress at the rupture front of the Chia-Yi earthquake was evidently large enough to have overcome the influence of fault heterogeneity and to have dominated slip amplitude there.