Negative beliefs rooted in past experiences, such as "I am unworthy" or "The world is a dangerous place", can persist over years and continue to influence how we approach similar situations. This thesis investigates whether Imagery Rescripting (ImRs), a technique in which individuals mentally revisit distressing memories and change their outcome, can reduce the convincingness of these encapsulated beliefs. Using a non-clinical sample, we tested whether expressing actions during ImRs that were previously inhibited or impossible (e.g., standing up for oneself) increases a sense of mastery, and whether this regained control helps explain why encapsulated beliefs become less convincing. Findings suggest that ImRs reduces belief conviction, with mastery potentially playing a key role in this process.