I usually keep rather good track of what leads me to a particular article. And if I want to mention something in these pages and there's no clearly discernible trail in my mail or someplace else in my files I'll devote at least a few minutes to a search to find that path. I'm a firm believer in giving credit to my sources, and those sources aren't only what I quote, but also what led me to what I quote. Thus if I write here that "I chanced upon" something, what I'm hinting at is that I no longer have any idea how I got to it and have expended enough fruitless effort trying to find the source.