The paper examines a modified real business cycle model of a small open economy such as the Korean economy. The model economy is assumed to produce output with two types of capital: traded capital and non¡ⓒtraded capital. Domestic individuals can borrow from the world capital market only by using traded capital as collateral, and investment in non¡ⓒtraded capital must be financed by domestic savings. It implies that the capital mobility is partial rather than perfect although domestic residents have free access to the world capital market. By incorporating externalities into the production technology, the model economy is able to generate dynamic path of equilibrium time series solely driven by non¡ⓒfundamental shocks such as animal spirits of investors or self¡ⓒfulfilling expectations if the ratio of traded capital to total capital is sufficiently high. The paper shows that the second moment properties of the Korean aggregate data could be reproduced in a modified real business cycle framework where fluctuations are driven only by non¡ⓒfundamental shocks, not by the disturbances to economic fundamentals such as technology. This requires a high value of traded capital relative to total capital, which means that the domestic capital market must be highly integrated with the world capital market. It implies that there exists some critical level of capital mobility beyond which the business cycles of an open economy becomes highly vulnerable to non¡ⓒfundamental shocks such as self¡ⓒfulfilling expectations.