This post first ran on the Children’s Cause for Cancer Advocacy website.

I once thought that turning 40 would be a significant milestone in my life. Like most people, I assumed that the act of marking time by focusing on the calendar was the main, fitting way to celebrate progress, the perfect way to celebrate life. My “landmark” birthday would surely be meaningful in its own right.

But many things happened on my way to 40. Experiences, both emotional and profound, rushed in and capsized my notions about which moments I would honor with my time, my attention and my memory. Instead of standing on deck, squinting toward the distant shore of an upcoming birthday, I gradually found myself celebrating moments that were organically swirling at my feet.

The awakening began with the birth of our first child, 12 years ago. Within 5 1/2 years, our brood grew by 3 more. In that intense and overwhelmingly busy time, I began to shed the idea that any one day was destined to be more relevant than all others just by virtue of its place on the calendar. Of course, a birthday can be a special, exciting time – for adults and certainly for children – but, in my life, the memories that have endured having nothing to do with candles on a cake. I don’t recall my 27th birthday, but I remember my first son’s toothless grins that appeared every time we played Somewhere Over the Rainbow. I’ve forgotten how I celebrated my 29th birthday, but I recall my second son’s childlike awe in the Museum of Natural History. Is my 30th birthday vivid? My 33rd? No and no. But I will always remember how adorable my daughter looked in her first pair of pink converse sneakers, as well as my 4th child’s very early ability to dance right on beat.

Becoming a parent was a powerful lesson, but it was only part of my education. In April of 2011, my husband and I were blindsided by the fact that our young son’s low grade fever, a fever that surfaced and abated several times over 2 weeks, was a symptom of something far more insidious than a virus or infection. At 8 years old, our child was diagnosed with acute lymphoblastic leukemia, and our world was turned on its head. But amidst all the worry and fear, I reaped the benefits of my ever-blooming understanding that there was magnificence in life’s more modest moments; suddenly, no other insight was more important or more true. My ability to hear euphony in a child’s unexpected, silly reaction or my appreciation of a deep connection built while explaining away a child’s fear were the most beautifully wrapped gifts I opened during some of my darkest hours.

August 6th, 2013, was chemo day for my son. It was also my 40th birthday. Sitting in the pediatric cancer center, bearing witness to incomparable levels of sadness and strength, no one aware that it was my big 4-0, I knew unmistakably that for 12 years I had been following an authentic map, one that had allowed me to unearth the real treasures in my world. On this map of life, the most meaningful milestones are not the days marked by birthdays or anniversaries, but those seemingly quotidian experiences I share with my children, my family, my friends — snapshots that, in reality, are not insignificant at all. Turning 40 paled in comparison to the brunch that I shared with my daughter early in the summer before she left for sleepaway camp; the walk I took with my eldest son recently, our arms linked; the fun basketball game I played with my youngest child; the way I was able to make my son laugh during that chemo week, even when he was feeling so horrible from the meds. I know that thosetypes of moments are the big ones — the ones that will most enrich the years I’m given and provide me with the fortitude to navigate the frothy, unforgiving waves that might crash against my vessel. Those are the milestones of a life well lived.