Our firstborn will be receiving his high school diploma on the stage of Boston Symphony Hall today. The ceremony will mark the end of four years of study and fun, a time of growth and learning for him. But this joyous event also carries another significance: the end of our time with him and, to a degree, his need for us.

There is something special about a firstborn. When he arrived, I suddenly and for the first time in my life understood what love meant. The feeling was instant and overwhelming, as though a portal had opened and I had spiraled into an entirely different universe. His arrival made my prior life seem so trite, irrelevant, and empty. Nothing that had come before him mattered.

I was lucky enough to work from home for most of his life, which enabled me to be with him as much as possible each day. I consciously made my own interests a lesser priority so that they would not be a distraction from time with him. I wanted to be there for whatever he needed. He was such a gift to us that I wanted to give him the gift of me—fully present, by his side, through all the glories and challenges of his childhood.

I can recall the moment clearly when I realized I had gotten the meaning of this time together completely wrong. I saw a father on a bike towing his son in a trailer. I remember thinking how great it was of this dad to do that for his son, and how happy his son must be to have his dad there. But when I looked at the boy, it hit me: he wasn’t paying attention to his father, but was focused on the world around him. The father was incidental to the boy’s experience.

That moment left me reeling. I realized that my time with my son was not a gift to him. He had been brought into this world and placed in our arms and felt our love and the security that brought, and then, as soon as he was able, he looked beyond us. We became an ever-shrinking part of his ever-widening world. The process of a child growing up, I realized, is one of slow but steady separation. Each day, more and more, as he discovered the world’s wonders, he would go farther and farther out into it, leaving us farther and farther behind. The time that I had with him was actually his gift to me.

We celebrated his milestones unaware that these small gains for him were our small losses that added up until the day we realized that, although he has not yet gone off to college, he has, in a way, already left us. Somewhere along the way of his childhood, something slipped from our grasp, and we would never get it back. That small hand that had always so tightly gripped one of ours had at some point, without notice, come free. We were returned to that time before he was born, which his arrival had rendered so meaningless. The moment of this realization is the moment the heart breaks.

We do deserve to pat ourselves on the back. When he arrived, he did not come with a manual. His arrival was, to me, a day of both joy and terror. I was in awe of this beautiful, delicate thing, yet so fearful of the mistakes I was certain to make. His walking across that stage today will validate a job well done, both on his part and ours. But his success in becoming an independent, self-assured, capable, kind, and considerate young man also marks a separation. I think it’s okay to acknowledge this aspect of his striding off confidently into his future. We can both celebrate him and his achievement while we mourn for what we’ve lost.