This presentation will first examine the differences between first and second language (L2) acquisition and explore their implications for second/foreign language teaching. From the perspective of language interfaces, it will then investigate why success in L2 acquisition is rare while failure is common, using the L2 acquisition of Mandarin intransitive verbs as a case study. Although the use of intransitive verbs is often considered relatively simple and straightforward, and is rarely discussed in detail in textbooks or grammar guides, English-speaking learners of Mandarin face significant challenges. An empirical study of L2 Mandarin acquisition by English native speakers, discussed in this presentation, reveals that learners encounter difficulties in mastering the word order of Mandarin sentences with intransitive verbs, even at advanced levels. While they can easily acquire the basic "NP + intransitive verb" word order, they struggle to understand the conditions under which the "intransitive verb + NP" order conforms to Mandarin grammar. Drawing on the interface between syntax and semantics, this presentation will analyze the performance of English native speakers in the empirical study. It will explore the constraints on their processing of the target language, their inefficient allocation of attention to various sources of information, and their challenges in coordinating and integrating information across multiple linguistic domains. Additionally, the presentation will highlight the importance of research on L2 Chinese acquisition in the context of international Chinese language education.