The memory is the first to go.
That is based on my experience. That's why things like this happen.
During my bookshelf spring cleaning, I discovered I had two copies of Paul Auster's book, The New York Trilogy. And I remember on one (or more) one recent occasion staring at a copy of this book in some bookstore and thinking to myself, I'll buy that next time. Not knowing that two of its ilk lie dormant, unread, and largely ignored, gathering dust, occupying prime prime realty space in my very limited bookshelves.
And look at the dates of purchase. Just one month apart. Short term memory malfunction.
And this is not the first time it has happened.
This kind of mistake only happens to books. I don't think that will happen to clothes, shoes, bags. Because I buy them less frequently and will not likely forget a purchase.
We can chalk that up to old age. Some may call that a desperate, rabid greed for books. I'd like to think I'm compensating dead trees, that they have not died for naught. And rescuing Paul Auster's reputation by not allowing his books to linger in the discount bins.
Things like this are what keep my Bookmooch inventory alive.