This text examines the historical and philosophical distinction between mere impression and true knowledge as defined by the Ancient Greeks. The author notes that while both humans and animals can be misled by appearances, Ancient Greek philosophy significantly deepened this issue by establishing a sharp contrast between opinion (doxa) and genuine knowledge (episteme). According to the Greeks, true knowing was only possible through insight or contemplation (theorein). The text emphasizes that even a correct opinion (orthé doxa) cannot be considered true knowledge because it lacks the certainty derived from a direct understanding of reality. This necessity to scrutinize even convincing impressions led to the development of rigorous investigation aimed at uncovering how things truly are. Once truth is perceived through direct insight, subjective impressions lose their relevance. The reflection highlights the epistemological foundations of Western thought and the critical importance of distinguishing appearance from reality in the pursuit of truth.