Some scholars have argued that the rise of digital media and a “high-choice media environment” have facilitated selective exposure and led to opinion polarization among the public. Others, in contrast, argued that digital media facilitate incidental exposure to news, connections with weak ties, and the building of heterogeneous networks. This article contends that the polarizing influence of digital media is not always materialized. Rather, the immediate political context matters, and polarization effects of digital media are particularly likely to arise in times of heightened political conflicts. This article analyzes survey data derived before and during the recent Umbrella Movement in Hong Kong. The results show that political communication via social media was significantly related to extremity of political attitudes only during, but not before, the Umbrella Movement. The polarization influence is applicable to both people with and without a clear political orientation. Interpersonal discussion and news exposure also had polarizing effects on public opinion during the Umbrella Movement, suggesting that polarization effect is not unique to social media when the political context itself is polarizing.