Halloween as we know it today has gone through a lot of changes from its origins. The holiday is now a mishmash of traditions from all over that have been adapted to the way we want to celebrate. The ancient Celtic Samhain was appropriated by Christians to make All Saint's Day, with harvest traditions from different places, supernatural stories, and fun ideas eventually incorporated along the way.
Check out a list of Halloween pictofacts at Cracked, many having to do with the holiday's history. It is labeled as 31 for the number of days in October, but you might notice that several have nothing to do with Halloween as a holiday. They are just scary. But that's the point of Halloween anyway, isn't it? We pull out the scary stuff to remind us that we can handle it, and then we celebrate it as a pleasurable rush of adrenaline once a year.