It started with a cookbook for babies, a book so fat with recipes that any new mother feeling the least bit overwhelmed would take one look at it and weep while contemplating the endless tasks before her. Now that my own children were old enough to use their words to tell me just how little interest they have in homemade (or any other) tahini, I considered passing the book on to a pregnant friend. But that seemed like an unloving thing to do.

So I offered it up on Freecycle.org, a website (with many local chapters) where people seeking to get rid of perfectly good items can find people who are willing to drive or commute to their homes to take them. I’ve unloaded all kinds of stuff through Freecycle, from placemats to toddler beds. I knew there would be many women perusing the site who would be happy to have the cookbook. One of them, probably sporting a sling and a smile, would take it off my hands. And then my bookshelf would have room for a different cookbook I’d probably never use.

Freecycle could not be more community-minded. It’s also a low-key competition, in which wooers of the free items try to sound charming or deserving or fun, to improve the odds that that old window screen or piano or discarded action figure (only one arm missing) will be bestowed on them alone. As an occasional benefactor, it’s my policy to go with whoever sounds the most certifiably sane, since this person will be coming to my home. Through email, I wrote back to the most polite requester that the cookbook would be on my front porch the next day.

Then I promptly forgot.

I was abruptly reminded by an email the next day: “So sorry – traffic a bear! Will be there just as soon as I can!” That would have been fine, except I was reading the email from my midtown office, while she was traveling all the way across the county to my home with a toddler and a newborn in tow, now hanging tough in traffic, all to pick up a book that wouldn’t be there.

I had betrayed the ethos of Freecyle, which is one of spontaneous generosity, accommodation and pay-it-forward neighborly kindness. I give a lot away on Freecycle, but I also have received bounty. Once, someone posted that she had a toddler pea coat that I could pick up. I packed up one of my sons and drove to an unfamiliar neighborhood in a town nearby; the homes got smaller and the cars more banged up as I approached my destination. My son in my arms, I walked up to the porch where I’d been told I’d find the coat. A gift bag awaited me, with a thick ribbon around the top; nestled inside in the tissue paper was a handsome blue, lined pea coat that had been pressed and folded. It was a gift, a lesson in the small graces of a life lived with care and consideration.

And now, my own mistake: What should have been a small, rewarding outing for the recipient of my cookbook instead would be an exercise in disappointment, an advertisement for my own thoughtlessness. Freecycle thrives on a sense of mutual responsibility – to the planet, to not clog its landfills with goods that others need; to ourselves, to live thriftily; and to each other, to make good on the commitments we make to strangers online. In this last regard I had failed, and I felt that I’d let down more than this one woman.

I emailed her my sincere apologies. I asked for her address so that I could mail her the book. But somehow I needed to do more. So I promptly emailed her a gift certificate; she could buy Super Baby Food and a copy of Dr. Sears’ tome on attachment parenting too, if she felt like it.

I was only compounding my own error. The beauty of Freecycle is that it has nothing to do with cash, and everything to do with creative resourcefulness. Is there any compensation lamer than a gift certificate? The young woman wrote back, graciously, that the drive was no big deal, and that she could not accept my generosity. I told her that the deed was done, but if she wanted she could pay it forward for holiday gifts; she finally accepted my apology and the certificate. And the next day, we agreed, she would come pick up the book, and it would indeed be there waiting.

All seemed fine. Except that when I came home, I saw waiting for me on the porch a small, beautiful bouquet and a thank-you card. I was of two minds. I was touched by the insistent thoughtfulness that Freecyle inspires. But I was pained that this woman – willing to drive across the county for a book she might have ordered second-hand for a few dollars online – had spent money to brighten my day or even things out. It was as if, in resorting to a gift certificate, I had broken the spell of Freecycle, its efficient and magical thrift.

I remember, months earlier, lighting up one morning as I opened my email and saw the subject heading: “They’re absolutely beautiful!” Thanks to Freecycle, some placemats my mother had foisted on me finally had found their way out of my basement into the home of a woman who had picked them up the night before. She was apparently delighted; I, in return, was rewarded with the most enthusiastic email I had possibly ever received. A lift all around, and not a penny expended.

I took the flowers from my porch and put them in a vase. I wondered what should happen next. Maybe, if I got the woman’s address, I could leave her a little something around the holidays, which were approaching; a plant, maybe. Maybe she’d surprise me in return with a knitted scarf. We’d never meet: two strangers trying to let the other know, through symbolic gifts, that we cared in some vague, indefinable way. It could go on forever, a mysterious tradition.

But I resisted the urge to up the ante. Instead I sent an email thanking her for her unnecessary kindness.

The flowers, I must say, lasted for more than two weeks. An assortment of mums whose stems I trimmed to fit in a short vase, they graced my dining-room table well past all reasonable expectation – beautiful, durable, natural and yes, in the end, exemplars of thrift.

Susan Dominus is a staff writer at The New York Times Magazine.