My husband and I are celebrating our 576th month wedding anniversary this week. In each of the first 100 of those months, we exchanged little greeting cards, a romantic gesture to mark the date and to celebrate our progress as a couple, much as teenagers do when they manage to sustain a relationship for more than a few weeks. While we were hardly teenagers, we were still young enough, and naive enough, to consider ourselves remarkable. “Hey! Another anniversary and we’re still married.”  This was, after all, the era of Woodstock, of free love and flower children; couples didn’t last very long, much less bother to get married in the first place.

Anniversary. The word comes from the Latin anniversarius, meaning “year” and “turning,” though anniversaries don’t always count years. People track daily, weekly, or monthly anniversaries of having quit smoking, for example, or of having maintained a dietary program. Birthdays are anniversaries. The remembrance of major events, personal achievement, national holidays — all are anniversaries of sorts. We even have words for anniversaries that become too numerous to count: centennial, sesquicentennial, bicentennial.

Not all anniversaries are happy, of course. Many mark catastrophes that have left death and destruction in their wake and emotional scars on entire populations: 9/11 comes to mind. Psychologists have a name for the grief and anxiety survivors often experience on or around the anniversary of a traumatic event or personal loss: “the anniversary reaction.”  Some people struggle openly with such reactions, while others may have only a vague idea, if any at all, why they experience a recurring malaise at certain times of the year.

Good or bad, happy or sad, what all anniversaries have in common is that they mark a remembrance and serve as a way of reminding us to not take anything, or anyone, for granted — not love, or life, or freedom, or security, and especially not the presence of those who are dearest to us. Gratitude for what we have while we have it may be the one true secret to joy in life, and the best antidote to experiencing debilitating loss and regret later.

So this week, my husband and I will celebrate our 48th wedding anniversary (in years), along with the “coincidental 48th anniversary of the Apollo 11 moon landing (a lesser commemoration, to be sure).  We will get all dressed up and go out for a lovely dinner at one of our favorite restaurants. Yes, we will exchange anniversary cards both serious and silly, and we will toast to our good fortune in being alive and well and together in love. And we will be grateful, because we know what we have is rare; we may no longer be young and naive, but we still consider ourselves and our relationship to be remarkable.

A lasting marriage is one thing, and there are all sorts of ways and reasons why couples stay together in spite of their problems and dissatisfactions. But a good marriage, a truly happy, fulfilling marriage, is something else again. Any marriage counselor will tell you that “marriage takes work,” work to develop the interpersonal skills required in any partnership. But actually, marriage takes more than that: it takes awareness. Relationships are never static; they grow or diminish, move in different directions “for better or worse.” The wedding ceremony isn’t the end of the courtship dance; it’s only the beginning. You have to pay attention if you want to keep dancing in the right direction.

My mother was widowed when I was a little girl, so I was raised by her and my grandmother. (Interestingly, my husband’s mother was also widowed when he was a boy, which probably accounts for why gender issues and divisions of domestic labor have never been points of contention between us.) Growing up, I was the only kid with a single working mother, so my models of the typical family were found in the homes of my friends with whom I spent so much time. Even as a youngster, I could feel the undercurrents and readily see that some marriages were better than others, that some homes were happier and more harmonious than other, and that the state of the marriage and the home were somehow related.

My best friend from 5th grade on was Judy, and she lived nearby on top of a small grocery store and gas station they ran. Her family, she, her parents and her two brothers, became my second family and have remained so for my entire life, though only Judy and one brother are now still living. Her mother and father, Mr. and Ms. P as I called them, had a very traditional marriage: Ms. P cooked and cleaned and yelled at the kids, and Mr. P worked long hours and was entitled to rest and relax when he got home. Everyone deferred to Daddy — but Mom called the shots.

These were not people of wealth and sophistication. They lived modestly, often frugally, but always with joy, generosity and gratitude. There was a love you could feel in their home, a genuine, palpable affection among them that welcomed and embraced everyone else. And there was humor, always humor, even in times of hardship and disappointment.

Judy and I grew up and moved away, she to the West Coast and I to the East Coast, but I stayed close with her parents who lived well into their mid-90s. On the occasion of their 70th wedding anniversary (yes, in years), they took a cruise to Alaska. They became quite the “celebrity couple” on the ship, and were honored on the last night at the Captain’s gala. The MC congratulated them on their anniversary and then asked for the secret to their long and happy marriage. Ms. P thought a second and simply said, “Just be nice.”

Mr. P didn’t have to think at all. “Just do what she says,” he replied.

And that’s how you have a happy anniversary year after year.