Why do I have this book?

The book is On Being Certain: Believing You Are Right Even When You Are Not, by Robert A. Burton, M.D., published in 2008 by St. Martin’s Press.

It arrived yesterday in a padded envelope with the return address “Salon Media Group.” There was no enclosure, no packing slip, note, order acknowledgment, nothing. Nothing.

The book looks interesting. In fact, it looks just like the sort of thing I do buy and read. And I will probably read it.

But—
— I have no memory of ordering it. In fact,
— as far as I know, I never heard of it before I opened the package.
— I checked my Amazon order records, and I did not order it there.
— I pretty much don’t order books elsewhere.
— If I really did order this and then forgot it, it will be the first time I’ve done anything so utterly absent-minded; there is no reason to think I’m that far gone yet.
— I haven’t done anything lately—signed up for anything, donated to anything—that was offering a book as an incentive premium.
— I used to have a Salon.com membership, but it lapsed.
— No one in my family ordered the book or had ever heard of it.
— All Christmas presents incoming and outgoing have been accounted for.
— The Universe has never before chosen the U.S. mail as a medium for delivering its messages to me.

I am stumped.

So why do you think I received this book?