On Jan. 1, 1967, at age 16, I began keeping a daily log book. I haven't skipped a single day since. Obsessive? Maybe, but I've also urinated every single day since, and nobody considers that weird.

To call the resulting 17,000-plus entries and 350,000-plus words a journal would be a tad grandiose. I keep it simple: what I did, where I was, who else was there, the occasional momentous news item, plus phenology facts such as last spring frost, first returning robin, ice-out date for the lake, etc. I reserve most editorial scuttlebutt for essays like this.

One value of the opus is its facility in settling arguments. Over the decades half-serious disputes have arisen over what we (friends, relatives, spouse) did on such-and-such an occasion, with everyone involved convinced that their recollection of details is correct. Finally, I say, "OK, I'll look it up," assuming, that is, that there exists agreement on what year and month is in contention. Checking the pertinent entry, we often discover we were all wrong.

That introduces two insights I've empirically reinforced via 47 years of logging daily events:

First, human memory is far more pliant and faithless than I realized. It's distressing how many times a vivid image in my head, say from 1969 or 1974, about who was part of, say, a certain canoe trip and where we traveled, is almost completely erroneous. My log establishes that specific people, events, times and locations become routinely jumbled in apparently random ways, and it matters not at all how crisp is my remembered picture.

Also, memory tends to embellish. As novelist Joseph Conrad wrote, "In plucking the fruit of memory one runs the risk of spoiling its bloom."

In other words, if you treasure a certain recollection, don't look it up.

Second, and the bright side, is that the first point doesn't matter much, since we forget almost everything anyway. It's intriguing (and distressing) to select an incidental month in 1980 or 1985 and read the log for every day of that four-week span. I did that? Then? With them? Well, I guess I do kind of recall, now that I see it mentioned.

It's clear that if I hadn't recorded it, the information would be lost. Apparently, routine amnesia is more than a plot device for soap operas. How big a deal that is or isn't depends, I suppose, on your temperament, or your philosophy. But if we are what we remember, and most people seem to feel that to one degree or another, then we appear to be far less substantial than we imagine.

And from the evidence of my log, I can only conclude that we routinely imagine — or at least modify — many "facts." Keep that in mind if you are ever on trial for a serious crime, and a witness against you begins their testimony with, "Yes, I remember seeing the accused …" At that point your attorney should leap up and shout, "Objection! The witness is a human, your honor."

A popular misconception likens memory to a video camera, dispassionately recording and storing data for later retrieval — a kind of digital cloud inside our skull. Neurological research shows that's not how the mind works. A better analogy would be to imagine that your brain hosts a slightly batty impressionist painter, fond of mash-ups, who is often free-associating while slinging paint onto canvases that are later stashed in different studios, or simply tossed in the trash. That's not all bad. It might be tedious and wasteful, if not maddening, if we actually recalled everything that ever came to our attention. Our memories are vetted and edited, though the standards of style are unclear.

I don't claim to remember why I initiated the project, and the log itself offers no clue, but now that the habit is ingrained, I understand I can't stop. It's a ritual. I'm never distant from a notebook nor often separated from a pencil. I've arisen in the middle of the night to augment an entry. I've urged others to take up the practice, opining that if you want to know where you are (or where you're going), you need to know where you've been; if you want to know who you are, it's useful to know who you were. That's another acute demonstration of the log: I'm not the same person I was 30 years ago. How could I be? I possess documentation that I'm doing different things with different people under different circumstances. My 1970s model was scrapped.

Yet some parameters endure. Philosopher George Santayana famously said, "Those who cannot remember the past are condemned to repeat it." Not precisely, perhaps, but human history, both personally and collectively, is definitely thematic. And if you didn't record it, you either won't recall it, or your memory of it will be faulty. Historian Barbara Tuchman wrote, "The unrecorded past is none other than our old friend, the tree in the primeval forest which fell without being heard." Perhaps that's why I launched the log — it made me seem more real. Or maybe the record is akin to scratches on the wall of a prisoner's cell, tallying the days until release.

But to benefit, you must reference the recordings. Back in 2003, I registered how astonished I was that the United States government was intent on invading Iraq. Didn't the Bush administration (and most of Congress, and most of the American citizenry) remember the history of the Vietnam War — only a generation past? Didn't they know the story of Iraq, a deeply sectarian, artificial nation created by the League of Nations in 1920? "History," said Norman Cousins, "is a vast early warning system." Accompanied, apparently, by a very faint alarm bell.

I read a lot of history and biographies, and given my daily jotting, I take particular notice of the numerous occasions when I see the phrases, "From his diary …" or "In her letters …" Of such raw material is the historical record constructed. Writing diaries and letters used to be a common practice, but how many do it today? I suppose the contemporary surrogates are e-mail files, social-media postings, blogs and other electronic formats, though they are uncomfortably ephemeral compared to old-fashioned hard copy — think, DOS and 5-inch floppy disks. As novelist and critic Stanislaw Lem noted, "Where do consequences lead? Depends on the escort."

If the implication is that every generation has to learn the hard way, eschewing history or simply forgetting, then we are traveling a rocky road. It's like we suffer from a collective dementia.

It happens that my mother suffered from extreme dementia — probably Alzheimer's disease — before she died. As our population ages, it's sobering to realize that 19 percent of the 75-to-84 age group becomes demented, and after 84 it spikes to 42 percent. As anyone who's dealt with a demented loved one knows, it's a horrible ordeal for all concerned. One coping strategy is to recognize and relish the brief moments when it's funny.

We were fortunate to get my mother into an excellent "memory care" facility where she was safe and consistently medicated, and where a high level of understanding pertained. Her residential unit was shared with four other elderly women. At lunch they'd gather around a table, each of them displaying a characteristic tic. My mother continually said to everyone, "I love you." Esther was always "waiting for the bus," loudly complaining, "the damn bus is late again!" Margaret opened the newspaper to the obituaries and read them aloud, over and over. It seemed choreographed, and the script didn't vary until one day, as Margaret droned on, my mother — with uncharacteristically furrowed brow — reached over, grasped the woman's shoulder, and said, "OK, that's enough now."

I chuckled. As if it were a cue, Esther favored me with a coquettish smile and purred, "You're a nice boy, come to my room." She took my hand and rose. Panic must have flared on my face, for one of the attendants suppressed a guffaw, and another smirked and tossed her head as if to say, go with her.

Esther pulled me along with surprising brio, and rarely have I been more spooked. We entered her room and she closed the door. Still smiling — now conspiratorially — she opened the top drawer of a bureau, and from a nest of underwear produced a Snickers bar. She gave it to me. My relief was intense. "Thank you, Esther. I love Snickers." She beamed. I assumed it was something she did in years past with her children and grandchildren.

Maybe that's why I keep the log — it helps me recall and tell stories. Will it be useful if I suffer dementia? I don't know, but it's reassuring to have a record. It's a survival tool. It grants me a keen appreciation for history, both personal and collective, and if we don't remember we aren't healthy, and never safe.

It sometimes hurts to remember; my log is not without sorrow. But forgetting can be fatal. Interestingly, if your heart stops, you are simply said to be dead, and timely, vigorous CPR may bring you back. But if your mind stops, if your memory vanishes, there is a modified term: brain-dead. It is assumed to be a worse condition.

Peter M. Leschak, of Side Lake, Minn., is the author of "Ghosts of the Fireground," "Letters from Side Lake" and other books.