It is quite irrational to believe that a cat can bring good or bad luck. Yet throughout the world many people do believe that cats and their colour and behaviour can influence our lives. The ancient Egyptians even worshipped cats and they had a cat headed goddess named Bast with a city dedicated to her. In certain cultures animals are held to be holy. Consider the cow, in ancient Celtic Britain it was a sacred animal.
Cows still are holy animals in some parts of the world, such as India.
Perhaps rationality has very little, if anything to do with superstition. Superstitions are the half-forgotten folk memories of our distant ancestors who really did believe in them. BATS Bad luck is foretold if you see bats flying and hear their cries. In the middle ages in Britain it was believed that witches were closely associated with bats. One ancient British superstition holds that if a child rides on a bear's back it will be protected from whooping-cough.