Every word in a title should be capitalized. It’s an acceptable form of capitalization and it’s super easy to remember. I don’t understand why most people don’t do it that way. Otherwise you have to memorize all these exceptions for which words can and can’t be capitalized. Who can remember all of that? What about “in,” “to,” or “on?” It’s just not obvious. It’s like putting a comma after the second-to-last item in a list.