(Editor's note: Gordon's mother passed away at home on Saturday evening May 2, 2015 while holding the hands of all her children.)

I was 6 years old when my heart broke for the first time. I was walking away from squealing kids who weren’t my friends. Recess, especially for first-graders, should be the day’s highlight, but for me it was a painful stretch where every second was two seconds too long.

Moving to a new town in the middle of my first school year was tough. Tougher than my mother advertised.

“You’ll make new friends and have lots of fun,” she said. Kiss on the nose. I took her at her word. But as that first week bled into the second and my recesses remained unsweaty and wordless, I doubted her judgment and, worse, her honesty. I’d harbored that fatal assumption, common with lavished kids, that the world outside the nest is much like the world inside. It never occurred to me that I would be invisible or that love outside had to be earned.

I shuffled along the pine straw path where the schoolyard edged into the woods with a loneliness so blistering I thought I couldn’t endure it. I kept my eyes down. When you’re young and sad, you learn the ground.

“I have something for you,” I said to my mom after school. I handed her an eastern oyster shell, common to the Gulf Coast, but so uncommon in my experience that I thought it was treasure.

My chattiness overtook me. I explained all the symbolism in the shell. How the shape represented my small foot. How the dark muscle scar was my big toe. How the narrow part where the shell trailed off into a channel of ridges represented the lonesome path I was on when I found it.

“It’s beautiful,” she said. “What is this gift for?”

“Because I miss you so, so, so, so much.” She cried slow tears I misunderstood for years.

Motherhood is not a thankless job. Most of us thank our mothers in small deeds when we’re young and in easy words when we’re old. But the immeasurable depth of motherhood is only felt when you enter the bittersweet suffering of parenting. A caring parent understands the crushing impotence of watching your child suffer the world. Those paths you have to let him go down alone.

I don’t know what makes one woman become a good mother and another one of similar circumstance a bad one, but I do know that every bad mother thinks she’s a good one and every good one thinks she wasn’t good enough. When I look back over my life, I’m ashamed of the adolescent that didn’t appreciate the sacrifice of the dark-haired woman who was once my world.

Six months ago, just before Halloween, my phone buzzed with my mother’s ID. I answered nervously, customary since my father’s health has become more fragile.

“Hey, son. Where are you?” She had that layered tone. Ominous bulk in a carefree envelope.

“A salvage yard. Looking for old light fixtures. Why?”

“Well. I just wanted you to know that I went in for a CT scan today. And it looks like I probably have cancer. I didn’t want to tell you until I knew something.”

Sometimes, a boy harbors the fatal assumption that the world cannot exist without the mother who created it.

“I’m so sorry, baby,” she said. “I’m so sorry to put you through this. We’ll find out more after a PET scan. Then we can choose the best path after that.”

That night, on my couch, I cried longer and louder than I have since I could count birthdays without reusing fingers.

My mother has responded well to treatment, but she is thin, weaker-voiced and concerned with loose ends.

When I was planning a Mother’s Day column, I went to my mom’s house to ask easy questions: What was the hardest thing about motherhood? What was the easiest? What is your favorite age? Did you always want to be a mother?

Then I asked her, of all the artwork and flotsam we’ve given her over the years, what is she most sentimental about?

She hobbled back to her vanity and came back into the room and gave me an eastern oyster shell.

“This.”

“Why?”

“Because you hurt so much and I couldn’t fix it.”

She asked me to keep the shell after she was gone. I agreed. But someday I will be gone and the shell will go back to being just another oyster shell dumped in a landfill or the woods. Maybe some other boy or girl will find it. They might even think it’s treasure, but they will never know the loneliness that shell represented to the boy who lost his mother once and is unready to lose her again.

The woman who clutched a rough shell to her breast and cried slow tears that I now understand.

Gordon Keith is a Dallas writer and broadcaster whose columns appear regularly in The Dallas Morning News. He may be contacted at gkeithcolumn@gmail.com.