In Italian superstition, Friday the 17th is traditionally considered unlucky because its Roman-numeral form can be rearranged to mean “I have lived.” The date is written XVII, which can be rearranged as VIXI, a Latin expression meaning “I have lived.” In funerary contexts, VIXI could imply that the speaker is dead, giving the number an ominous association.
Friday also has negative associations in Christian tradition because the crucifixion of Jesus is traditionally placed on a Friday. The combination of Friday and 17 therefore became especially unfortunate in Italy, much as Friday the 13th is viewed elsewhere.
The belief is cultural rather than a prediction supported by evidence. Italian buildings, hotels, and airlines may still avoid the number 17, although practices vary by region and person. A common mix-up is assuming Italy shares the English-speaking world’s Friday-the-13th tradition; Italian superstition more characteristically singles out Friday the 17th.