That's one of the mysteries of the Universe. A few years ago a University tried to solve the question, the project was to send a man and a woman into a shopping mall in New York, the spec was to buy a pair of trainers. The man went in, went straight to the relevant shop, bought a pair of trainers and was out in a quarter of an hour. The women went in, visited just about every shop, came out two hours later, laden with shopping and no trainers? You work it out.