AbstractIn El Niño‐Southern Oscillation (ENSO) dynamical predictions, the ensemble members may show a large spread, leading to low prediction accuracy. The reasons for unreasonable forecast spreads in dynamical predictions are investigated based on hindcast/forecast results from the North American Multimodel Ensemble system. A category of failed‐forecasting members is defined if a negative Niño34 index in winter is forecasted by one member for the observed El Niño events. Compared with reasonable‐forecasting members, the failed‐forecasting members show significant cold sea surface temperature anomalies (SSTAs) in the southeastern Pacific (SEP). Such cold SSTAs can be traced back to the initial cold error in the SEP region. The initial cold error can be enhanced by positive feedback near the SEP region and further hinder warm SSTAs in equatorial regions, leading to a failed prediction. This result highlights the essential role of the SEP region, providing possible contributions to enhance the ENSO forecast skill.