Historically, how frequently do truly exceptional "great comets" appear, bright enough to capture widespread public attention?

About once every decade

While comets generally become visible to the naked eye about once per year, these annual visitors are often faint and require patience or optics to confirm. A truly 'great comet'—defined as an object exceptionally bright, capable of capturing widespread public interest outside of astronomical circles, and remaining visible to the naked eye for months—is a far rarer phenomenon. Historical observation suggests that these truly exceptional events occur, on average, approximately once every ten years. Comparisons between past spectacular sightings and more recent ones reinforce that a major, well-known display is often a generational event, perhaps arriving every 10 to 20 years.