A hypothesis : once upon time a primitive e.g. a homo Neanderthal or a homo sapiens that lived in a primitive village was devoured by a black panther and some primitives that were his companions, when they saw that, then they had spread around that black cats bring bad luck.
But these are "ypolepses" (false suppositions i.e. painful memories with mythical stories that are mixed with the fear of death) and not "prolepses" (preconceptions or anticipations or intuitions i.e. pleasurable memories with real fact stories without being mixed with the fear of death).
And here is the ending paragraph in the letter to Pythocles in which Epicurus describes the procedure of the manifold way of the Canon, and on how, we can be able to separate the imagination from the reality since the real purpose is living without agitation i.e. the pure pleasure.
"All these things, Pythocles, you must bear in mind; for thus you will escape in most things from superstition (mythical stories) and will be enabled to understand what is akin to them. And most of all give yourself up to the study of the beginnings and of infinity and of the things akin to them, and also of the criteria of truth and of the feelings, and of the purpose for which we reason out these things. For these points when they are thoroughly studied will most easily enable you to understand the causes of the details. But those who have not thoroughly taken these things to heart could not rightly study them in themselves, nor have they secured the end for which they ought to be studied".