Writing makes you think about boundaries. How much to reveal. How much to hold back.

Never mind writing. All it really takes to think about boundaries is living in the world with other people.

Sometimes you want to talk to them. Sometimes not. Some friends you can confide in. Others, forget about it. Someone smiles. Somebody smirks. Our boundaries. Shift.

Moods, rules, roles, affection, competition. Each moment of every relationship, unique as a swirling thumbprint.

A hundred or so years ago, some parents actually subscribed to the adage, “children should be seen and not heard.” Shut up, kid. Now there’s a boundary for you.

But they didn’t call it that a hundred years ago. Back then, a boundary was, you know, a fence, a border line, a barrier. Crossing one entailed known rules and risks. These days, though, you can’t pick up an advice column or a self-help book without coming face-to-face with references to the blurrier boundaries of the emotional kind.

Take for example the comment that Carolyn Hax, my favorite advice columnist, made to “Snoop,” who wrote last November to ask about a message he’d found while checking his girlfriend’s email. Her reply: “Snooping, obviously. Serious boundary violation.”

He read her email. Bzzt! Boundary violation! Could it be any clearer?

Like when you’re at the optometrist, and she’s — Click. Click. — switching the lenses in front of your eyes —This one? Or this one? — and suddenly — Go back! That one! — the bottom line is finally in focus?

It’s the same with a great metaphor. After all, the bottom line is rarely distinct when events are in motion. But when you can view moments through the lens of just the right metaphor — they suddenly become clear. As a bell. Ding!

Like boundary. Such a useful term. I did a little googling to find out when it entered our vocabulary in the psychological sense, as opposed to the fence sense. From what I could see, a few psychiatrists were starting to use it in the 1970s, mostly in reference to psychotic behavior. But as far as popular, non-psychotic parlance goes, it doesn’t seem to have made much of a blip on the cultural radar screen till the late ‘90s and early 2000s. Practically now.

So what took us so long? I wish someone had thought of it sooner. I could have used it. I mean, I really needed it.

A few years ago, I wrote a book, The Year of the Bird, which, if you read it, you already know that it includes a story about my 22-year ex-marriage to my ex-husband, a world-class yeller, punisher and tyrannical enforcer of arbitrary rules. One way to sum it up is to say that he lacked boundaries.

Unfortunately, I wasn’t able to say that. Because I’d never heard the word “boundaries” used that way. Of course, insufficient vocabulary was not the reason I stayed with him for so long. There was a whole tangle of stupid reasons for that, topped by the big three, self-blame, self-doubt and shame. It was only years later that I learned to look at his behavior in terms of boundary violations. Even then, long after it was over, aside from the nightmares and the PTSD, it’s helpful to be able to understand those years in these terms.

Another thing that’s helpful is talking about it. Telling your story. Which in this case is not easy. For one thing, I still feel embarrassed, mortified, humiliated about staying with him so long. I mean, wouldn’t you? Of course. Anyone would have had more sense than that. Except me.

For another, talking about it is a real conversation-stopper. No one knows how to respond. Awkward. At best.

That’s where writing comes in. That marriage is a subject that will puzzle me as long as I live, and what I love most about writing is the way it helps you figure things out.

For instance, when you’re talking and run out of ideas, you can just stop and say, “I can’t think of anything else” or “I forgot what I was going to say next.” Writing doesn’t let you off that easy. I mean, have you ever read a story that ended with the line, “I can’t think of anything else. The End?” Me neither.

Writing forces you to lash yourself to whatever thoughts you had and ride them all the way through the storms to the end of the trail. To try to hammer some sense out of the stories you need to tell.

The author E.L. Doctorow wrote this: “Writing is like driving at night in the fog. You can only see as far as your headlights, but you can make the whole trip that way.”

All right then. Once more, into the fog. Over the boundary. Here goes.

There’s a story I’ve been carrying around for a long time, since the tail end of the last month I lived with my ex-husband. It took place on a hot, muggy night in late May, 1990. He’d long since stopped working and spent most of his time in his home, um, office, drinking, or roaming the other rooms, yelling. I was a freelance artist, always busy, lots of deadlines. My office was in the basement of our house. Trying to keep the boundaries clear between work and home was, as you might imagine, challenging.

Anyway, there’d been an “incident” between us earlier that day, during which I’d driven over to my parents’ house, where I was planning to spend the night. My ex called their house and promised he’d leave me alone if I came home and locked myself into the bedroom. I was reluctant, but knowing I had a deadline the next day, I drove home, locked the bedroom door, put on my nightgown and climbed into bed.

I’ll give you a few seconds to take that in. Are you still with me? Ready to get back to the story now? Okay.

Lying there and reading, or trying to read, I could hear him stumbling, drunk, around the kitchen, knocking into chairs, yelling on the phone, calling to order a pizza and leaving the house.

After about a half hour of quiet, the phone rang. I had an extension by the bed and picked it up. Hello?

A guy at the other end of the line asked, “Did a man from your house order a pizza from Domino’s a little while ago?”

Yes. I think so.

“Well,” he said. “He was just in here. He was really angry. He looked like he was going to hurt somebody. And I just wanted to make sure it wasn’t you.”

Thank you, thank you, thank you! Thank you! I thanked him profusely and quickly, pulled my jean jacket on over my white nightgown, stepped into my black loafers, threw my toothbrush into my purse, pulled out my car keys and ran out the front door into the thick, muggy dark.

And my car wasn’t there.

He’d taken my car.

I ran across the street, and just a few steps beyond the corner, I heard the buzz of an engine from over the hill. It was my car. It was him in my car. Even on a night as inky as that one, I knew my white nightgown would stand out like a flag. I ducked behind a neighbor’s van and stayed there till he’d gone into the house with his pizza.

As soon as the front door shut, I raced up the hill to the shopping strip a couple of blocks away. Despite the late hour, High’s, a small convenience store, was still open. I went in.

Sweaty, wild-eyed, out of breath, hair frizzy as static on a TV screen, dressed in my white nightgown and black loafers, I stood among the brightly lit aisles, trying to emulate the attitude of a casual midnight shopper whose most pressing decision is whether to purchase twinkies or cheese doodles, yoohoo or mountain dew.

It would have been funny, if it had been funny. But it’s hard to feel the humor when a rack of Doritos is the only barrier between you and a man so angry that the pizza guy actually called you, instead of the other way around.

I should explain here that this was in the time before cell phones. And we were in the suburbs, where everyone has at least one car, so taxis are as rare as, say, peacocks.

But, believe it or not, just at that moment, a taxi drove up and parked right in front of High’s open doorway. The cab driver got out and walked into the store. I can only imagine what he thought as he saw me approach. But if he sensed something amiss, he never let on. When I asked if he could drive me to my parents’ house in Bethesda, he said yes.

He drove the few miles down the interstate, calmly resisting my repeated entreaties to speed, and deposited me in my parents’ driveway, where I thanked him and gratefully handed him the thirteen dollars I had in my wallet.

I had a key. I let myself in. My parents woke up, we talked for awhile, and eventually we all went to sleep. Thousands of other things happened later. But that’s the story I want to write tonight.

A story about boundaries. The boundaries the pizza guy sliced through. I mean, rain falls down, not up, right? And in just the same way, we call the pizza guy; the pizza guy does not call us. Sure, he never fails to ask you for your number when you phone in an order. But has he ever actually called you? Ever? I thought not.

But this pizza guy. He did. He found my phone number and he called me, even though he didn’t know me or anyone else who might have been at home. He called because he wanted to make absolutely sure there was no chance that anyone might get hurt that night by the angry man who’d just picked up a triple cheese, triple pepperoni pizza.

There’s a name for that kind of pizza guy, for that kind of person. That’s right. Good Samaritan. Which he truly was.

But things were moving so damn fast the night our paths crossed that I never stopped to get his name. I wish I had. I wish I’d thought of dropping by Domino’s a few days later and asking who’d worked the late shift that night.

I wish I could hurdle back over the boundaries of time to find out who he was, so I could send him a card or flowers or maybe buy him a dinner other than pizza. So I could thank him again. And let him know how very much his intentional act of kindness will always mean to me.

So before we say good night, let’s review. Preserve your boundaries. Respect those of others. Don’t ever trust anyone who tells you they won’t hurt you if you lock yourself into the bedroom. Turn off your headlights in the fog; they just make it harder to see. And always say thank you to the pizza guy.