I’ve never been very good at sharing. Growing up an only child, I didn’t really have to be. I actually have three sisters whom I adore—but technically, they’re half-sisters, from my father’s previous and subsequent marriages. There’s a big age difference between all of us—we range from 50 to 21—and we’ve never lived together. So for all intents and purposes, I grew up an only child, never truly having to share. My older sisters weren’t exactly clamoring to get their hands on my Smurf collection, and by the time my younger sister was old enough to care about Smurfs, Smurfs were painfully passé. Sure, I had lots of friends and play-dates, but it’s easy to be magnanimous when you know that the person you’re sharing with will be picked up after dinner, at which point your belongings go back to being filed in the “Mine, Mine, Mine” Department.

When it came to food, the concept of sharing was even more foreign to me. I was one of those picky eaters who strikes fear into her parents’ hearts by subsisting for weeks on little more than a handful of cheerios a day. Thus I not only never had to share my food, but I was practically given a standing ovation whenever I deigned to put nutrients into my mouth. I was curious, but befuddled, when friends with siblings would recount fights over the last slice of pizza, or about how at breakfast they would lick the cinnamon bun they most coveted as a way of claiming ownership. How terrible, I would think. I could have any cinnamon bun I wanted, and as many to boot.

Despite my lack of actual experience as a good sharer, I advised lots of young, impressionable minds on the necessity of the trait, as a camp counselor for many summers and a nanny for almost two years. But if any of those little kids had ever asked me one simple question—“Why?”—I would have been rendered totally speechless. I had no idea why they—or anyone—should share. As far as I could tell, sharing was a bum deal; it meant getting less of what you wanted. It was something one should do, but not something anyone would want to do. Luckily, no one ever did ask me, and therefore I didn’t poison any young minds with my clueless ideas about sharing. My lack of skill in the sharing department might have remained as such, if not for my partner Joseph—a divorced dad—and his three children. My stuff wasn’t really an issue for Joe’s kids—they were about as interested in my collection of 1960s-era Italian VHS tapes as my older sisters had been in my Smurfs. It was more a matter of food. So help me if, at a restaurant, mine was the only entree to arrive with french fries. Three pairs of eyes would turn in my direction; I could practically hear their stomachs growling. Succumbing to defeat, I would reluctantly push my plate forward, and all that would be left for me after the flurry of little hands would be the undesirables—the overcooked, the underdone, and those weird little twisted burnt ones. On a hot summer day, all I had to do was take out my monogrammed L.L. Bean water canteen, and three pairs of parched lips would part, followed by at least one hoarse refrain of “I’m thirsty.”

I defended myself accordingly. As someone with a lifelong predilection for super-sweet cereals, I fretted that the children would consume all of my Froot Loops, and I actually hid them in a box of boring, whole-grain cereal, where no one would ever think to look for them. Including me. Imagine my feeling of foolishness and, yes, shame, when weeks later, having quickly gone through a box of Cocoa Krispies, I resorted to the healthy stuff and found a bag of stale Froot Loops instead. If all this makes me sound really selfish, I think it’s because I was being really selfish. All the times I had issued a perky “Let’s share!” to one of my babysitting charges, it had been just lip service. I had no idea what I was talking about. The stale Froot Loops provided a wake-up call. I noticed how great Joseph’s kids were at sharing with each other. Maybe children with siblings suffer licked cinnamon buns or sacrifice that last slice of pizza, but they become very good at looking out for each other’s needs. When Joseph and I welcomed our own son into the family, my stepkids astonished me with their generosity, both with actual things like teddy bears and cupcakes as well as the more abstract, like time and love.

I finally had the answer to the question I hadn’t ever been asked: Why share? The answer is actually very simple. Sharing is a way of looking out for your fellow human beings; it’s a way of seeing that everyone gets what they need. Sharing my food with Joe’s kids was never about me getting less, it was about making sure the kids had enough. Bearing that in mind, I realized that not only had I been bad at sharing, in some ways I’d been a lousy stepmom, too. Fortunately for me, they are not only generous children, but forgiving, too. Now when I cheerfully pass my canteen, without being asked, on a sweltering summer day, my stepdaughter takes a long drink—but leaves enough for her brothers—and says to me, “Good sharing!”

Of course, she doesn’t know yet about my secret stash of Cocoa Krispies. Old habits die hard.