Since the beginning of the XIXth century, a conviction has prevailed in the Polish historiography according to which in the second half of the XVIIIth century a Piars` craft school existed in Opole Lubelskie. This school was the subject of numerous historical texts starting with those written by Józef Łukasiewicz in 1851 and ending with those of Mariusz Ausz (2009). The historians underlined it with pride that the existence of this school was a significant and glorious fact. Most authors of encyclopedia articles and dictionary entries always mentioned this craft school. However, even a superficial analysis of the historical sources concerning this “school” leads to the obvious conclusion that the Piars` craft school in Opole Lubelskie has neither ever been established nor has it ever educated any students nor has it ever started to perform its didactic activities, which means that it has never existed. It was only an idea that has never materialized. It is a myth, not an historical fact. The case of this school – or rather of this idea – illustrates how myths have been created in historical sciences and how these myths can advance to axioms taken for granted by all and how historians themselves can contribute to it. This is a perfect example of how easy one can be self-deceived and how careful one should read source documents.