Earth's tropical regions drive some of the most powerful weather and climate variability globally. Among these, the Madden–Julian Oscillation (MJO) is a dominant intraseasonal climate signal, characterized by large clusters of clouds and rainfall that slowly move eastward across the warm tropical oceans. In doing so, the MJO shapes rainfall patterns, influences tropical cyclones, modulates monsoons, and even impacts weather far beyond the tropics. Understanding the factors that govern its speed and intensity is therefore essential for improving subseasonal to seasonal climate forecasts.