But what helped more was his temperament. Our son, Angus, is an exceedingly happy and social baby, eager to interact with his parents and strangers alike. As the months passed and his tools for engagement with the world sharpened, so did his indiscriminate enthusiasm for people. He smiled at everyone we passed, at the curmudgeonly men on the bench on the corner, at the intimidating-looking guy on the subway blasting music on his phone — who, to my shock, smiled back. Once he could stand, he would Houdini out of the shoulder restraints in his stroller and stand, arms flung out like Kate Winslet on the prow of the Titanic, reaching out to pedestrians, embracing the world.

Last July 4, I took him to the neighborhood playground. Angus had recently learned to walk, so instead of squeezing him into a swing, I let him scamper around the jungle gym. My habit at the playground is to keep mostly to myself, mumbling small talk with the other dads only when not speaking at all would be more awkward. At 13 months old, my son had none of my reticence.

He toddled up to a few older boys, his eight teeth beaming, hoping they would play with him. They ignored him — few 6-year-old boys want to hang out with a baby — but he kept following them around, either too ignorant to understand he was being spurned or too resiliently good-natured to let it sink him.

He certainly won’t be able to maintain that degree of vulnerability his entire life. The cultural pressures of masculinity, the scar tissue of inevitable failures, the demonstrations of what happens to men who reveal weakness will make him more clenched, tensed, numbly severed from himself. In the meantime, though, I nurture his softer side, showering him with affection, encouraging him to hug and kiss, praising him more for his sweetness than his strength.

As Angus chased the boys around, I imagined giving a sentimental wedding toast for him a few decades hence in which I observed that, typically, the child sees the parent as a role model, but how on the playground that day, I thought of Angus as the one for me to emulate, an example of how to embrace with open arms a world that is often indifferent and sometimes cruel.

All my feelings for my infant son — and the inexorability of time’s passage, of life coming full circle — swirled together through this hypothetical speech, and I felt myself starting to well up, simultaneously watching my 1-year-old on a jungle gym while wondering who he would be as an adult. In my hazy projection, he had figured out how to be a man with a certainty that has thus far eluded his father.

The other dads were still nearby, and so, with my usual hackles raised, I didn’t let myself cry. But I almost did.

Teddy Wayne is the author, most recently, of “Apartment.”