I would estimate that the average book at The Library survives being borrowed about 30-35 times. After that, they either have to be replaced or repaired; if they're out of print and damaged beyond repair, they're lost forever after what seems to be a pretty brief life span. Here are some examples of books that met an even untimelier death:

Borrowed 15 times: Spine broken, pages missing, back cover torn off.

Borrowed 26 times: Pages loose, some missing.

Borrowed 7 times: Pages 265-438 missing.

Borrowed 14 times: cover torn, book ripped from cover.

Borrowed 22 times: General wear, water damage, spine damaged.
Roughly every month I find about 20-30 books from the subject of English language and literature in this condition on my desk, and I have to decide whether they should be replaced, repaired or thrown away.
Novels are in much worse condition than academic books.
Do you think this has more to do with the way the books are handled, or the way they are constructed? Seems to me that pages used to be sewn into hardcover books, whereas now they are frequently glued.
A combination of both, but mostly handling, because if you notice that a book is poorly bound, you can still handle it in such a way that it doesn't fall apart.
Books #1, #4 and #5 are hard-bound and sewn, and that didn't protect them from being damaged. #2 seems to be a case of weak binding (or rather gluing). In the case of #3 it's really impossible to tell if the missing 200 pages were lost or simply torn out.
Makes me drop all my nonviolent attitude when I see how some people treat books that are not their own.
Certainly there is no excuse for mistreating books, and I remember, when I was in college, students complaining that they could not access needed articles because they had been ripped or cut out of the bound copies of the journals; not just careless behavior but criminal.
I also remember that my high school textbooks were sturdy enough to survive being thrown down flights of stairs, (I being a mere witness to this heinousness), without seeming much the worse for wear; the covers didn't come off, nor the pages fall out...
And my older daughter, who is a computer software specialist in the publishing industry, told me that she and her colleagues are of the opinion that book publishers are using ever cheaper glue and less expensive binding techniques, this being apparently something they have discussed.
I think there are some people who just cannot accept the idea that books need to be handled with more care that was required in the past, and in some cases pages are deliberately removed.
I wonder if it is possible to purchase books with "library binding," and if so, if the sturdier books would last long enough to justify the added expense.
Some US publishers still offer books in "library binding", but most of them don't any longer, and German publishers never offered this kind of thing at all.
I know that I'm a kind of neatness freak, so I'm certainly not representative at all, but I would feel terribly bad if I didn't return a book to the library in exactly the same condition that I received it in.
Okay...I'll bite. Being a librarian, I'd like to see the actual research HarperCollins used to determine that 26 loans is the average lifespan of a book. I suspect that the number is too low, but without seeing how that number of loan events was arrived at, cannot be certain. Is it a legitimate number arrived at through unbiased and thorough research? Or is it a convenient number that, coincidentally, happens to mirror the number of times a library with a 14 day loan period could expect to circulate a new, popular monograph in the first year?