Political scientists generally consider that the incentive for legislators to switch parties lies in their desire to be re-elected. While some scholars attribute defection to the legislators' popularity and strong connections with their constituents which enable them to be re-elected without relying on party labels, others assert that legislators switch if they perceive that staying put might threaten their chances of re-election. In this paper, we find that the two assumptions, to some extent, contradict each other. More surprisingly, the two contradictory hypotheses cohabit under the single non-transferable vote (SNTV) system. From an analysis of the switching in the Taiwanese Legislative Yuan, the empirical evidence shows that because of fierce intraparty competition in the multimember districts, not only barely elected but also top-ranked legislators switched party affiliation in order to avoid the loss in votes or even seats to their copartisans and to maximize their chances of re-election.