This article examines a hitherto neglected aspect of the expansion of international trade in nineteenth-century East Asia—that of how ordinary people understood changing trade patterns. Rather than the political debates and imperial competition that have been the focus of existing research, I use the diary of Sim Wŏn’gwŏn (1850-1933), a farmer from Ulsan, southeastern Korea, to assess how knowledge shaped Sim’s perception of, and response to, the international grain trade. Sim used his diary to develop an economic worldview based on his observation of cyclical, seasonal changes in the weather, harvests, and prices. While this enabled Sim to anticipate some fluctuations, the international rice trade posed a challenge as local market prices began to reflect events beyond Sim’s sphere of information. I argue that uneven access to knowledge influenced Sim’s participation in international trade, which in turn cannot be understood without reference to Sim’s existing understanding of the economy.