The effect is particularly powerful because each new poster is a suprise. The passer-by does not expect to see new content each time they see a poster with the same message, and becomes curious as to what and where the next variation will be. By using variations on the same basic visual structure, the subsequent posters catch the eye thanks to their repeated elements, but draw closer attention by their new content each time. The message is reinforced by having been read three times in succession, but is richer and more thought-provoking because of the varied content.