Predicting the development of rip channel systems on beaches is relevant for beach safety, nearshore mixing and dispersion, and has been puzzling researchers for decades. Field observations and computer simulations have focused on predicting the spacing and growth time of rip channels as a function of wave characteristics. A satisfactory predictor of rip channel spacing and growth time has not yet been proposed. Here, we show that the lack of predictability of rip channels is an inherent property of the system related to the high sensitivity to the bathymetry prior to pattern development. Sensitivity to the initial cross-shore profile appears to be as important as sensitivity to wave height. Although we might be able to predict rip channel characteristics, the information required by such predictors will need to account for the underlying bathymetry. Implications arising from this study are that other geomorphic patterns could display similar sensitivity.