Past research demonstrates that first language (L1)-like competence in each language can be attained in simultaneous acquisition of bilingualism by mere exposure to the target languages. The question is whether this is also true for the "weaker" language (WL). The WL hypothesis claims that the WL differs fundamentally from monolingual L1 and balanced bilingual L1 and resembles second language (L2) acquisition. In this article, these claims are put to a test by analyzing "unusual" constructions in WLs, possibly indicating acquisition failure, and by reporting on analyses of the use of French by bilinguals whose dominant language is German. The available evidence does not justify the claim that WLs resemble L2. Instead, it shows that WL development can be delayed, but does not suggest acquisition failure. Finally, reduced input is unlikely to cause acquisition failure. The fundamental issue at stake is to explore the limits of the human language making capacity.