<p>Episodic memories are segmented. This study explores the dual role of prior knowledge in event segmentation, hypothesizing that knowledge leads to coarser segmentation when experiences align with it, and finer segmentation when they do not. Participants underwent a training phase to learn sequences of images, followed by a segmentation phase where they identified event boundaries, and, finally, a surprise memory test. Our findings reveal that trained participants segmented less at trained color transitions compared to untrained participants. Conversely, when sequences were disrupted, trained participants exhibited more segmentation. Interestingly, the segmentation differences changed over time, suggesting that participants updated their expectations based on new experiences. Additionally, our study dissociated the roles of prediction errors and context switches in event segmentation. While prediction errors alone would predict larger differences between trained and untrained groups, we observed high segmentation rates in the trained group, even for expected transitions, underscoring the importance of contextual shifts. In conclusion, our results highlight that knowledge is a double-edged sword in event segmentation, promoting both coarser and finer segmentation. These findings provide insights into how the mind navigates and organizes experiences, emphasizing the nuanced interplay between knowledge, perception, and memory.</p>