By the time we reach our 50s, most of us have experienced a moment when, for the first time, we truly confront our mortality, a moment when it suddenly and forcefully comes home to us that we ourselves personally actually are going to die — as in: be dead — someday. This revelation can be produced under varied circumstances: It happens for one person upon the death of a friend, a contemporary; for another while he or she reads “Four Quartets”:

We are born with the dead:

See, they return, and bring us with them.

The moment of the rose and the moment of the yew-tree

Are of equal duration.

(“Little Gidding” ll 230-3)

In my case, the moment of terrible certainty about my own death came not as a moment of the rose or a moment of the yew-tree but rather as the moment of the box of staples.

I was rummaging in a desk drawer searching for the always elusive roll of “forever” stamps and for some reason I paused to read what was written on a box of staples I saw there: “Swingline standard staples / fits all standard staplers / 5,000 staples.”

Five thousand staples. Five thousand? That seemed like a lot of staples.

I lifted the box and found that it was quite heavy. Looking inside, I saw that about three-quarters of one strip had been used. Since the box also helpfully informed me that each strip contained 210 staples, I could estimate that I had used about 150 (mathematically alert readers will note that 210 does not divide evenly into 5,000, but let’s leave that aside). So: 5,000 take away 150 leaves 4,850. Four thousand, eight-hundred fifty? That, too, seemed like a lot of staples.

With a strange sense of foreboding, I worked some figures. Assuming that I had owned the box for a decade, which seemed conservative, then I had been using on average 15 staples a year, or one and a quarter staples a month — that seemed to pretty fairly reflect my propensity to fasten sheets of paper together with short lengths of bent wire.

I then asked myself how long it would take me, at the rate of 15 a year, to use up the remaining 4,850 staples. A calculator is supposed to be in this same drawer, but it is never returned there when people borrow it, so I used the one on my computer. The answer came out to 323 years.

That’s when I realized that I was going to die: I owned more staples than I could possibly use in my lifetime, or several of my lifetimes.

In fact, it was worse, because in another drawer I found two other near-full 5,000-count boxes of staples, one of which had to date from before 1986, because the box showed that Bostitch — formerly the Boston Wire Stitcher Co. — was owned by Textron, and 1986 was the year that Textron sold it to Stanley. (I dug this information up. In fact, the archaeology of my staple collection raised several interesting questions: Why, for example, does Swingline on one box promote its “sharp point” staple as having superior “penetration and clinching performance” to the “chisel point” staple, but on the newer box identify the staples as “chisel point”?)

Nothing says “mortality” like the realization that you will live only long enough to use up 3.2 percent of your office supplies. (The older boxes each had about 4,500 staples, which makes a total of 13,850; if I lived 30 years and used 15 a year that would be 450, or 3.2 percent.)

I can’t help thinking about what else I own that will outlast me: the jars of salsa and pickles in the back of the refrigerator; sheaves of legal-size copy paper; shoe polish; books.

Books. I have been blithely buying them all my life without ever giving a thought as to whether I will live long enough to read them. But will I?

I am not in any way a collector of books, but I am an accumulator of them. Counting shelves and estimating an average number per shelf, I figure that my bookcases hold about 4,250 books. In addition, I own more than 100 books on my Kindle, and there are at least a couple of hundred in boxes in the basement. Let’s call it 5,000 books (that number again) in total.

How many of my books have I already read? That’s a delicate subject. I hold that by simply owning a book I deserve about 90 percent of the credit I would get if I also read it, but not everyone looks at things that way. I am a little shocked to discover that on any given shelf, I seem to have read, according to the conventional standard, only about one-third of the books.

That leaves around 3,300 unread books. If I read one book a week … but you and I know that I don’t read one book a week, I read a couple a month, grazing in a few others. If I read two books a month, it would take me 137 years to read those unread books. So there we have it: absent the discovery that those long-lived, underfed mice thrive equally well on a diet of vodka and peanut M&Ms, I am not going to live for 137 more years, and therefore I do not have enough time left to read the books I own. Death will intervene (thank God) well before I get around to the later volumes of “A Dance to the Music of Time.”

We can look at this another, equally pessimistic way. If I die in 30 years, when I will be 85, and if I read two books a month, then I have 720 books left to read in my entire life. That number seems so … numerical. So low. Far too few slots remain in my life for anywhere near the number of books I want to read. Now what am I supposed to do when I go into a bookstore? Buy only books in the humor section because they are always extremely short?

I have heard that if you measured life by number of heartbeats, normal mice live as long as we do. So I wonder whether, if I ran around stapling pieces of paper together, even just random opened envelopes, so that I used up all my staples, I would not effectively extend my life by hundreds of years. Similarly, if I read one book a day, and instead of rereading “Franny and Zooey” for the 50th time read books I own but have never read, like “Terror and Consent” by Philip Bobbitt and Hermann Broch’s “Death of Virgil” (both of which, by the way, I think I deserve huge credit for simply owning), maybe I could also extend my life by a lot, although, admittedly, not in the somewhat pedestrian chronological sense.

Staples, books, pickles … When do you realize that you are going to die? When you realize that, in the remainder of your life, everything is countable.

James Collins is the author of “Beginner’s Greek,” a novel. This article is from Private Lives, a series of personal essays offered by the New York Times at nytimes.com/opinionator.