I would agree. I think most do start out with a grain of truth, somewhere. It's just a matter of finding out what it is. I think the ones that are truly fabricated, or have no basis in reality, don't last.
There are so many out-there stories about where I live, its hard to figure out which is real and which is our local history. Generally, the more absurd, the more likely it is to be true. After all, fictional stories have to make sense.