“Even if you decide to have just one drink, it’s easy to get into the next one,” Mr. Gilat told me. “The third one is calling an Uber and giving the kids to your wife or your husband or your friend. It’s the one that everybody is intimidated by, or afraid to admit that they’re having.”

In “Three Glasses Later,” the photographer Marcos Alberti documents the effects of three glasses of wine on subjects in his studio; the portraits reveal people moving from the stress and sobriety of the after-work hour to, well, a great many moods. “The third glass,” Mr. Alberti notes, “is about mayhem.” It leads you to a place where everything is unreliable, including the decisions you’re capable of making.

So it’s not just about counting the drinks — it’s about the number where each of us becomes untrustworthy. What am I no longer capable of in the shift between one number and the next? We are conditioned to think about that third drink as it pertains to driving, but it goes beyond how we get home. Most of us don’t like to recognize problem drinking as a possibility within our own orbit, or the toll it can take on our emotional, family and work lives. The truth is you don’t have to be a binge-drinking alcoholic for drinking to be problematic.

Numbers have always been key to our understanding of alcohol: The Aztecs called their gods of drinking “centzontotochtin,” or the “four hundred rabbits,” representing the myriad ways intoxication could make a person feel and act. It is entertainment, social lubricant, creative stimulant, sensory experience, delicious beverage. At the end of a long day, it feels like a reward. But at some point — maybe it’s falling asleep at 7 while getting the kids to bed after a couple of beers, or going to work for the third day in a row feeling vaguely muffled — signs start pointing toward too much.

And when it comes to knowing your limits, the baseline is always shifting. Mr. Gilat and others say that the regular reset is how they stay on speaking terms with the limits they started with. “It can mean a couple of days, weeks or months off from drinking to come back to that baseline,” he told me. The pause isn’t a punishment, but a check — a way to remind yourself that you can get by without drinking, that you can still fathom the responsibilities of life as a parent, partner, worker, friend. And that the pleasures of those roles are still palpable.

WE can expect that when it comes to recommended allowances for alcohol, the numbers will continue to change. The public-health pendulum swings frequently in this country, and guidelines vary greatly among countries. France appears to have no government-sanctioned limits. Britain, which has some of the highest rates of heavy drinking in the world, recently revised its limits downward; the government cites an increased risk of certain cancers. And yet, as the American addiction specialist Stanton Peele has observed, “despite being heavily outdrunk by the English, we have almost exactly twice their levels of diabetes, cancer and heart disease.”