My mother, when she was in her last years, had a habit of sitting in her chair, her hands on the arms, her fingers lifting and pressing down, one by one, as if she were playing scales on the piano. She’d never played a piano. In fact, she had no musical talent at all.

She was a soft-spoken sort, long on patience and kindness and compassion. She believed in the Golden Rule. She was a Christian woman who endured my father’s temper and my battles with him until finally both he and I saw how wrong we were and became the sort of men she deserved to have in her house.

But I was telling you about her fingers and the way they went back and forth, up and down, as she sat quietly in her chair. Upon first glance, at least the way I’ve presented this detail so far, it’s an ordinary moment that I’m describing: my mother sitting in her chair, looking at the television, the lamplight falling over her. How many times had I seen her like that, enjoying a moment of rest? She was a third-grade teacher for thirty-eight years, and after her retirement she worked in the laundry and the kitchen of a nursing home. Somehow she managed to help my father on our farm, and to keep house, and to raise a son. Why should I remember this particular moment?

Those fingers and the way they moved. Such a small detail, ordinary, barely worth noticing, unless you’re her son and all this happens on one of the last days your mother will know you.

Her dementia had worsened after a series of small strokes, and she wasn’t able to live by herself any longer. I was her only child, and I’d had to make the decision nobody wants to make, that she should live in a nursing home. I’d seen her move her fingers like that before and never thought a thing about it. It was just a habit she had, the same way she knelt by her bed each night and prayed before going to bed, or the odd way she had of accenting the syllables of certain words: Ca-SHEW, Il-LUS-trated, To-FU. Or the unique way she answered the phone with a rousing, “Yello.”

Those fingers, up and down and back and forth. Suddenly, though I’d seen her move her fingers that way countless times, I understood that she knew this was one of the last nights she’d spend in her home. Something was at war within her, something most likely that had to do with her belief in civility and the fear she felt. She worked those fingers to keep from saying something she’d regret.

On the night I’m recalling, the mail carrier had mistakenly delivered a parcel meant for someone down the street. My mother insisted on taking the parcel to her neighbor. By this time, it was dark. I told her not to worry about the parcel; I’d make sure it got to the rightful recipient the next day.

That’s when she clapped her hands together. The noise startled me. “All right, then,” she said. “If it doesn’t get to where it’s supposed to go, I won’t be the one to blame.”

I remember how her voice shook with anger, how tears came to her eyes. There we were at one of the extraordinary moments that will be with me as long as I live. I can’t forget it. I can’t ever forget how my mother insisted on doing the right thing at a time when she must have felt so wronged and wounded. I can’t forget the jumble of emotions that rose up at me when she clapped her hands and said what she did.

Memoirs are made from moments like this, those moments that shake us, perplex us, change us, or give us opportunities that we don’t take and they go shooting past us forever, never to come again. But memoirs are also made from the commonplace, from ordinary details that provide a backdrop from which the unforgettable moments emerge. My mother’s fingers, the clapping of her hands, the accusation that she made: all of that exists alongside the crossword puzzles she liked to do, the shopping lists she made on the backs of calendar pages, the Halls cough drops she kept in her purse, the deliberate way she shuffled a deck of cards, the Dear Abby advice columns she liked to read. Every ordinary detail of the lived life is necessary to the extraordinary moments that we remember, that haunt us perhaps, the ones that demand our attention when we set out to tell the tale. We have to pay attention to the commonplace so we’ll better recognize the variations within it. Sometimes a simple action signifies everything if we’re watching closely enough.