Well-educated and prosperous, Asians are called the “model minority” in the United States. However, they appear disproportionately underrepresented in leadership positions, a problem known as the “bamboo ceiling.” It remains unclear why this problem exists and whether it applies to all Asians or only particular Asian subgroups. To investigate the mechanisms and scope of the problem, we compared the leadership attainment of the two largest Asian subgroups in the United States: East Asians (e.g., Chinese) and South Asians (e.g., Indians). Across nine studies (n = 11,030) using mixed methods (archival analyses of chief executive officers, field surveys in large US companies, student leader nominations and elections, and experiments), East Asians were less likely than South Asians and whites to attain leadership positions, whereas South Asians were more likely than whites to do so. To understand why the bamboo ceiling exists for East Asians but not South Asians, we examined three categories of mechanisms—prejudice (intergroup), motivation (intrapersonal), and assertiveness (interpersonal)—while controlling for demographics (e.g., birth country, English fluency, education, socioeconomic status). Analyses revealed that East Asians faced less prejudice than South Asians and were equally motivated by work and leadership as South Asians. However, East Asians were lower in assertiveness, which consistently mediated the leadership attainment gap between East Asians and South Asians. These results suggest that East Asians hit the bamboo ceiling because their low assertiveness is incongruent with American norms concerning how leaders should communicate. The bamboo ceiling is not an Asian issue, but an issue of cultural fit.