"They grow up too soon," everyone told me. Eighteen years later, I finally understand what they meant.

It's nearly the end of summer break and my son goes out with friends. Ten minutes after he leaves home, I receive his text: Here. It's the same message I've received hundreds of times before -- our agreed-upon shorthand to reassure me, and probably him, in some still-unexamined way, that he has arrived safely at his destination. In a matter of days he'll head to college, and this routine, along with many others that have framed our days and nights, will come to an end. Reading that text triggers images stored safely away in my memory, a tiny flip book of our lives together.

My constant companion of nine months emerges with his eyes wide open. He's placed on my chest. I feel his heartbeat reverberating（回弹，反射） through mine. All I see are beginnings. Friends who visit caution that time is elusive（难懂的） , that he'll grow up faster than I can imagine, and to savor every moment. But I can't hear them; it's all too clichéd and my child has only just arrived. He's intoxicating: the beautiful bracelet-like creases in his wrists, the way he sounds like a little lamb when he cries. I'm filled with a renewed sense of purpose, of hope, of love. The first few months after he's born are topsy-turvy -- day is night, night is day. When sleep finally returns, so does work. My business suit is tight, my mind preoccupied. I pump milk in a cold, gray bathroom stall.

His teeth begin to appear. Baby bottles give way to solid foods. He points high above his chair to the clock on the wall. "Clock," he says. It's his first word, minus the "l," and it makes me laugh. Soon he is walking, skipping, making angels in the snow.

I'm promoted at work. It becomes harder to find the time to make playdates（上映期） and pediatrician（儿科医师） appointments. At lunch I read books about nurturing, teaching, inspiring your child. He calls my office with the help of his babysitter. "Momma," he says, "I'm making you a present."

The tooth fairy arrives and leaves him handwritten notes. He discovers knock-knock jokes and learns how to add, subtract, and read. He builds giant castles with giant Legos, rides his shiny bike down a country road with his feet off the pedals.

I quit my job to do freelance writing -- everything from training programs to marketing brochures（小册子） to essays - usually when the rest of the family is sleeping. There's never enough money, but now at least we have time.

Saturday nights are always family nights, spent at home. There are countless sporting events. He tries baseball, soccer, and track, then falls head over heels for basketball. He swings from tree limbs, wears superhero costumes, develops crushes, friendships, and fevers.

I volunteer at his school: cut, paste, read, nourish, fund-raise, chaperone. I like this job.

There are marathon bedtime story rituals, endless questions about how things work, and monsters under the bed. Lego pieces grow smaller and castles more intricate. He tries the guitar, plays the trombone, saves quarters to buy video games, and collects trading cards, which he keeps in a shoe box under his bed.

We get a dog. He loves this dog with all his heart. The dog loves him back.

One day his height surpasses mine and, seemingly the next, his father's.

He reads an essay by a sportswriter. It lights a fire in him. He starts to write his own stuff, wandering into my office as I try to juggle（杂耍，欺骗） freelance assignments.

I feel privileged to read his work.

Orthodontics are removed to reveal straight pearly whites. He earns his first paycheck as a baseball referee（裁判员） but wishes that it had been as a writer.

He learns to do the laundry, scrub the bathroom, and make pasta, though he often professes to forget how to do all three.

He turns 18.

On a cold and rainy Election Day we head out together to vote. After two hours waiting in line, he's the only teen in sight. It's not lost on him -- by the next morning he has written all about it.

He gets a job as a blogger, then starts his own website. And all the while there are macroeconomics（宏观经济学） , physics, and college applications.

The flip book's down to its last pages.

I've defined myself as a mother for 18 years. Who am I now? I look in the mirror. In my quest to help him grow wings, I forgot to grow some of my own. Can I find a new sense of purpose, rechannel the love?

Before I was a mother I was a daughter, infused with energy and the unspoken reassurance that my parents would always be there. But I can't be a daughter again. I'm on my own.

Does purpose -- mine, yours, anyone's -- require someone to nurture it, or is it inherent in all of us?

I'll soon be putting these competing theories to the test.

As I sit down to write this piece, I receive his text: Where are you?

Here, I text back.

For now.