A few months ago at a supermarket, with a snowstorm on the way, I realized what is so terrifying about motherhood. It had to do with locked shelves and a sea captain in 1926.

Bear with me.

Where I live, worrying about snow begins about a week ahead of the storm. I usually do my food shopping the first time I hear television newscasters losing their minds over the weather map. But I didn’t get to the store early this time, and I knew I was in for a long wait at the checkout.

In front of me, against the wall, was something I’d never noticed before — a large series of caged shelves, secured with a padlock. It was full of baby formula. That’s all, just baby formula.

I wondered if the supermarket got tired of so much of it disappearing from the baby aisle and locked it up here, in plain sight of everyone, so desperate mothers couldn’t slip a canister or two inside their bulky winter coats. I pictured those women in my mind, women who might steal, frantic to get home to a hungry baby. And that led me to the sea captain.

Ninety years ago Captain George Fried struggled to keep his ship afloat in a fierce January storm in the Atlantic. He received a weak distress call from a sinking British freighter and set out to find her. In blizzard conditions over the next 85 hours, the captain tried several times to rescue the crew of the sinking ship. When it looked hopeless, as it did many times throughout the rescue, he sent them this famous message: “I will not abandon you. I will not abandon you.”

When my first baby emerged from me, the doctor gently placed him on my stomach. I instinctively grabbed onto his squirmy body. He looked at me. And there. Right there. The single most terrifying moment of motherhood hit me.

Before that instant, I’d walked away from lots of stuff in my life. I’d stopped corresponding with friends who no longer suited me. I’d left boyfriends to deal with their broken hearts. I thought nothing of leaving projects half completed, conversations unfinished, and relationships in ruins. There was nothing to it.

That moment you become a mother, you tell your baby lots of things. Even if you’re just holding him and not saying anything aloud, you find yourself making promises you never made before. “I would steal for you. I would brave freezing water for you.”

And as the list goes on, you realize the one thing that will not happen. The thought arrives in whatever language you speak: “I will never, ever abandon you.”