This paper investigates the obligatory syntactic process in Hakka called ”verb reduplication”, of which a verb is reduplicated when followed by a CP headed by the clitic do. By providing an OT-based analysis, this paper argues that the syntactic operation is triggered by two ABUT constraints. When a verb takes a do-phrase to further describe its denoted action, if there exists another constituent in-between the verb and its following CP, attaching do to either the verb or the intervening constituent violates one of the ABUT. Hence, the verb must be reduplicated to create a structure that fulfills the requirement of both constraints. Contrastively, if the do-phrase immediately follows the verb, attaching do to its preceding main verb does not violate any of the ABUT. Here, the disallowance of verb reduplication can be captured by the Obligatory Contour Principle (OCP), which functions as a crucial syntactic condition to block reduplication, knowing that its occurrence would cause the adjacency of two identical verbs.