The world is full of secrets.

Not the regular kind, the kind told privately to one person via email and then accidentally broadcast to everyone you know when you hit “reply all” by mistake. I’m talking about secrets we’d love to share and in fact try to share, but no one ever believes us.

Want an example? “Enjoy them while they’re young, because before you know it, they’ll be grown.”

Older people often attempt to share this truth with young parents. The older people are usually strangers who come across the parents in the grocery store. The parents are trying to shop while the children are crying or arguing or running off with the grocery cart with the baby in the seat.

My younger daughter was a shrieking, screaming baby in the seat one Father’s Day years ago. In fact, the tantrum started because I insisted that she be the baby in the seat and not the baby in the cart itself, down there with the apples and the bananas and the cereal boxes.

The din was considerable, I don’t deny, and I was hurrying to finish up and escape when a man approached me.

“What is the matter with that child?” the man demanded to know.

“She wants to get into the cart and I won’t let her,” I told him. I didn’t think he was about to offer sympathy, and he didn’t.

“Well, it isn’t very nice for the rest of us to have to listen to!” he said.

Now, let’s say at this very moment a strange woman had paused with her cart to say, “Enjoy them while they’re young, because before you know it, they’ll be grown!” Would I have believed her? Would I have said, “You are so right! I’m going to pick up this red, kicking, furious baby right now and give her a big hug!”?

No, I would not. In fact, I might not have heard the woman at all over the baby’s screaming and the angry man’s shouting, and then I was too busy crying to truly appreciate my good fortune.

Of course, not all moments with my children were as tempestuous as that. Very few of them were, at least in retrospect. Still, when a person is in the thick of diapers or third grade or swimming lessons or any of the myriad stages of parenting, the idea that this will be over before she knows it is theoretical at best.

And yet, it’s quite true. The raging baby in the shopping cart went home, took a nap and grew up. It happened before I knew it.

These days, I watch parents and small children in the grocery store and feel the urge to say those very words. “Honest! It’s true!” I’d add.

I don’t bother, though, because I know they’d never believe me.

Another secret: Running makes you feel good.

I stumbled across this secret a quarter of a century ago, a few weeks after I took up running. I was no late-blooming Olympian; running a few miles made me feel like I was going to throw up and then die. But one day after a run I realized I felt ridiculously, crazily good. My daughters were both with me at the time, and I mentioned it to them.

“As awful as running is, I must say I feel good right now,” I said.

They didn’t believe me, of course. No one believes it. Runners have come right out with it, talked about the “runner’s high,” and the endorphins that cause it, and still they get nowhere. Non-runners laugh indulgently or else suspect a trap designed to trick them into adopting a good habit, and even euphoric runners finally throw up their hands and drop the subject.

My daughters watched me run for months without expressing the slightest desire to join in, although they both became runners eventually. My older daughter, who had often illustrated her opinion of running by pointing her finger down her throat, was a runner by age 13. For years we ran together, sometimes for hours, and often, as we sprinted the last few blocks, we discussed running’s Big Secret: If you feel bad, running makes you feel better. If you feel good, running still makes you feel better.

But try telling that to a non-runner.

One more secret: Dogs are comforting.

Dog lovers know this. We don’t adopt dogs for the sheer altruistic satisfaction of giving a needy animal a home. We take them in because they’re human cheerleaders. No, they’re supportive coaches. No, they’re four-legged confessionals.

In fact, they’re all of these and more. They root for us; they think we’re swell; they understand and forgive us no matter what and they don’t refuse to be seen with us if our jeans are too short or if our last haircut made us look like a poindexter.

All animals are comforting, in fact. There’s nothing like saying hello to a curious goat to lift my spirits, and coming across a sleeping cat while I’m wandering through a bookstore is my idea of bliss. But dogs are the best, because dogs not only like us back, they live in our houses and ask us to play and, just when we need comfort, they rest their chins on our knees or push their foreheads against our legs.

But people who don’t care for dogs shudder at the very thought of canine contact. When a dog approaches, they raise their hands and step back. And should a dog jump up — “I don’t pat dogs who jump up,” a visitor once told me. He might as well have said, “I don’t kiss babies who wear diapers.”

Dogs — even misbehaving dogs — are comforting, I want to tell such people. The love of a dog makes you feel like a good person.

But what’s the use? People who don’t like dogs never believe this, and why would they? I’d feel the same if someone told me, “You’ll love tarantulas! They’re so cuddly!”

So it’s a secret. Go ahead and spill it if you want. See how far it gets you.

Write to Margo Bartlett at mbartlett@thisweeknews.com.