Kepler and Galileo are well-known as two of the few Copernicans that promoted the notion of heliostatic astronomy in the early Seventeenth century. Kepler endorsed Galileo's new discoveries made through the telescope and was eager to establish a relationship with Galileo. But contrary to every reasonable expectation, Galileo always remained aloof from Kepler and never accepted Kepler's laws of planetary motion and his tidal theory. For a long time, this has been ”a maddening puzzle in the history of science”. There are many historical explanations as to why Galileo did not credit Kepler. This paper attempts to appraise the known interpretations and provide an alternative explanation for the mysterious and distant relationship between Kepler and Galileo. The alternative can be a supplement to other explanations. It also shows that the two Copernicans had their own ways of philosophizing, especially in their concept of the causation of motion, which led to Galileo never appreciating Kepler's scientific notions.