Countless young writers have asked the unanswerable question: how to write about family members without wreaking havoc? How to approach the urgent and inescapable material that has shaped your life without rendering that life unlivable – because you have included too many details about Aunt Joan or (almost always) portrayed one or more of your parents in an unflattering light … Given that fiction is always on some level born of experience (even when set in another century or on another planet), and that experience so often involves family, how to write fiction at all?

For years – decades, even – I skirted the question. I wrote fictions in which nobody I knew could find themselves, and when they did, it was pure projection. After I published The Emperor’s Children in 2006, three women asked why I’d written about their husbands, referring to one of the characters, a prominent journalist named Murray Thwaite, who was also a philanderer. They seemed reluctant to accept my assurance that I hadn’t. Convinced by small details – Murray’s preferred whiskey; his attitude towards teaching; his refusal to let the family’s housekeeper clean his study – they eagerly, if unhappily, claimed him. It turns out you don’t need to write about people for them to think that you have.

Over the years, when asked by students about the quandary, I’ve jokingly pointed out that Eugene O’Neill left Long Day’s Journey Into Night effectively in a drawer until his mother had died; or have suggested that in spite of profound upset over publications, most families reconcile, eventually. I’ve argued that each of us must write what’s most urgent to us. I’ve urged writers to write fearlessly, and to repress any publishing considerations until after the writing is done. I believe in that advice; but it’s also true that once a manuscript is finished, our impulse, most often, is to share it. If, as Stendhal famously suggested, a novel is a mirror walking down a road, we want our peers to see that mirror, and to recognise what’s reflected in its face. We want others to feel, and to say, “Yes, I see!”

This impulse may stem from multiple sources, but chief among them is surely the comfort of that recognition, the hope and reassurance that each of us is not alone on the planet, that our experiences overlap and can be shared, that we can both bear witness to our own lives and the lives of others, and also, as importantly, that this witness can be shared. In another novel, The Woman Upstairs, I suggested that an artist is ruthless, that she will plunder the lives of those around her for her art. “Ruthless”, though, is a way of speaking; “courageous” might be another way to frame the same idea. The distinction lies in intention. “Ruthless” implies indifference to others’ suffering; “courageous” may be an optimistic spin on what looks to others like airing dirty linen, but what if one’s intention is loving and compassionate? What if one’s intention is to see clearly, without condemnation, and to understand? As Chekhov wrote, “You would have me, when I describe horse thieves, say: ‘Stealing horses is an evil.’ But … it’s my job simply to show what sort of people they are.” This, I’ve always believed, is what fiction can do, what fiction does best: not to offer pious answers but rather to open questions, to illuminate what life is really like.

So when, finally, I came to write a novel that draws on my own family’s history, it was indeed in this spirit – wanting to bear witness to lives now gone, lives that were never of themselves dramatic or, in society’s terms, important, but that, in their flaws, contradictions, joys and disappointments, were meaningful – at least no less meaningful than anyone else’s. These lives – of my grandparents’ generation, born effectively with the 20th century; and of my parents’ generation, born in the Depression, less than a decade before the second world war – were inexorably shaped by larger historical circumstances as well as by temperament and choices.

Nobody wants to be engulfed by war, still less so when far from home. How any of us will behave in times of crisis is hard to predict. For the British, it’s a crucial narrative that they (unlike the French, the Belgians or the Dutch, it goes without saying) would have, if invaded, fought the Germans to the last; but as Madeleine Bunting’s The Model Occupation (1995), an account of the Channel Islands in wartime, makes clear, what really transpired when the Germans invaded British territory was significantly less glorious than the hypothetical myth. When my French grandfather – the naval attaché in Salonica at the time of the fall of France – heard De Gaulle’s BBC rallying speech on the radio in June 1940, he worried chiefly about his adored wife and children, from whom he was separated and with whom he couldn’t communicate, and only briefly and flickeringly contemplated making for London and the Free French. Instead, he followed his superiors’ orders and returned to Beirut.

When the Algerian war of independence broke out in the 1950s, my aunt, Denise, was at university, studying law. She wanted simply for her life to continue unchanged – a life in which she laughed with her girlfriends, flirted with boys, groused about her homework. A friend, reading the draft of my novel, suggested that I make the Denise character more politically aware, less preoccupied with fashion and food – “Surely,” she insisted, “she wouldn’t have been so oblivious!” And yet I know, from family correspondence – from letters she wrote to my father, who was then studying in Amherst, Massachusetts – that my aunt, on whom the character is based, made no mention, ever, of politics. Just as Flaubert’s Frédéric Moreau, in Sentimental Education, passes the barricades of 1848 with his mind on a picnic with a woman, so too many of us live alongside history, enmeshed in it but unaware. “Where can we live but days?” Philip Larkin asked, and days are comprised of toothbrushes and blisters, of birthday cards, dirty dishes, bills and laundry. Our daily horizon is rarely world-historical.

Does it constitute a betrayal to write characters, who, in ways that resemble my own relatives, reveal themselves less than ideal, motivated at times by fear and insecurity, by selfishness, or by any of a host of other human limitations? Again, I return to the writer’s intention – in this case, to my own. While I wanted all my life to write a novel about my family’s history, I couldn’t have written it until now – not simply because my grandparents and parents are no longer living, but because I needed to reach a state of clarity where I could see them not as my grandparents and parents, entangled in the emotional complexities of our familial lives, but rather just as people, like you or me, with ideas, dreams and disappointments, muddling through the way we all do, no wiser and yet no worse than the rest of us.

In his retirement, my French grandfather wrote, for my sister and me, a lengthy family memoir that covers 1928-1946 – from my grandparents’ marriage to the end of the second world war. My parents held on to many family letters, from the 1950s onwards. Preparing to write my novel, I read all these papers, and in so doing, heard anew the voices of these people that I love so much and so complicatedly: when he penned his memoir, my grandfather wrote to me as the future adult I wasn’t, yet; my parents wrote to one another as the hopeful and amorous young lovers that they were before I was born, then as tired and sometimes frustrated new parents, and so on. They reveal themselves in what they choose to share, in the language they use, in their private jokes. In their letters, they’re still alive – I felt it so powerfully, reopening airmail envelopes untouched since, say, 1953, read (by me) perhaps for only the second time ever, hearing their voices in my head. It was, for me, a joy to read what they wrote and to write this book; it is, profoundly, an act of love.

For what, if not for this, did they save the letters all their lives? For what did my grandfather – who in his youth aspired to be a published writer – write his memoir, which he called Everything That We Believed In? In order, I believe, that someone might see them clearly, might try to understand. And because I am a writer, in order that I might hold up that mirror, as I walk down the road, in the hope that others, too, may see themselves reflected – in the toothbrushes, dirty dishes, unpaid bills, in anguish and in love, in the stuff of days.

• This Strange Eventful History by Claire Messud is published by Fleet. To support the Guardian and Observer, order your copy at guardianbookshop.com. Delivery charges may apply.