Could repeatedly “exercising” the creativity muscle help build up creative performance over time? To answer this question, we conducted three longitudinal studies with a total of 830 participants, resulting in the generation of 17,652 creative solutions and 39,211 unique product names. In study 1 (and its replication), we uncovered contrasting effects of practice on creativity. While daily practice fostered convergent creativity, divergent creativity showed mixed effects — the number of unique ideas generated remained stagnant, and the average novelty of ideas decreased with practice. In study 2, we found that repeated practice affected divergent creativity through two opposing forces: practice hindered the activation of less routinized routes (and thus hurt the number of unique ideas generated) but also positively affected the fluency of the routinized routes (and thus increased the number of unique ideas generated). Interestingly, the vast majority of participants inaccurately predicted that repeated practice would uniformly facilitate both types of creativity.