Although shared leadership is typically considered a beneficial leadership approach, findings reporting its effectiveness are mixed. By integrating implicit theory and the "Too-Much-of-a-Good-Thing" (TMGT) effect, this study hypothesizes that both too little and too much shared leadership restrict team creativity and employee creativity. We test such double threshold logic across three independent studies. Study 1 results reveal that shared leadership can promote team creativity, but only within a certain range. Results from Study 2 suggest that shared leadership is positively related to employee creativity, but again only within a certain range. Study 3 replicates the findings of Study 1 and Study 2, and reveals that shared leadership is unrelated to employee creativity when team collectivism is high. Together, these findings suggest that there is a double-threshold effect of shared leadership on employee creativity and team creativity, and that the double-threshold effect of shared leadership on employee creativity is moderated by team collectivism.