It wasn’t the love story that made me cry. In the British director Joanna Hogg’s fourth feature The Souvenir, the central relationship – the one that takes up most of the two-hour screen time, the one we are supposed to care most deeply about – is the one I cared about the least.

We are supposed to feel for the protagonist, the naive and hopeful Julie, caught in a relationship with a charming older man, Anthony (Tom Burke) who holds within him a tragic secret. We are supposed to catch our breath at that relationship’s twists and turns, the withholding looks and the furtive behaviour. And yet the relationship in the film that I felt most deeply, that reduced me to sudden, unexpected tears in a barely-filled Light House cinema screen, was the one between Julie and her mother.

Julie is played by Honor Swinton Byrne, and her on-screen mother by Honor’s own mother, Tilda Swinton. So, the familial bonds hold strong on and off screen. We would know Tilda’s androgynous, unscrutable face anywhere, but Honor is new to us (the director has known both for many years, but cast Honor after a chance meeting which made her realise her ideal lead, the one she had been searching for months for, had been in front of her the whole time). Compared to her mother, Honor’s face has an openness about it that feels without artifice – you know she’s, well, a real person as opposed to a Hollywood actor. The lines in the film were mostly improvised, and Honor wasn’t given a script. Instead, she got a character outline and Hogg’s diaries and notes from her early filmmaking days to read. Honor plays a version of Hogg, the young 20-something film student Hogg trying to find her place in the world. Julie is Hogg’s avatar, but she’s her own person too.

What hit me so hard in The Souvenir is how it depicts parenting: the delicate touches, the throwaway comments, the unquestioning love even when hard questions are being asked. Julie is truly loved by her mother, and this is a plain fact. And she loves her mother back, though at 25 you might not really know how much you love the person who raised you.

The most emotional scenes in The Souvenir, the ones that had me wishing I had a tissue secreted somewhere in my over-stuffed canvas bag, the ones that made rivulets of black mascara tears run down my face, were the ones between Julie and her mum, right towards the end of the film. They are in Julie’s Knightsbridge apartment, together, waiting for Anthony to come home. He’s very late. Julie doesn’t want to go to bed, but her mother gently convinces her it’s time for sleep, in the way only a parent can. The camera follows as they carry out the same ordinary nighttime routine that you probably carried out with a parent or loved one many times growing up. Where you’re ushered into your bedroom to get changed, and where your parent lifts up the duvet for you to get in. Then they tuck you in and whisper their goodnights, in whatever special language you share between you. All is safe in the world at that moment – you are loved and cared for. You can relinquish your responsibilities and worries.

In the film, Julie might be an adult, but she is still tucked in by her mother. We don’t see the action – we only hear it, our view obscured by the half-closed bedroom door. The way Julie’s mother speaks to her reminded me of how my mother speaks to me, even now, when popping in to say goodnight to me when I’m in bed at home in Cork. She does not tuck me in, but I’d wager she would if she could. That I’m in my thirties and not a child hasn’t quelled her need to protect me. The terms of endearment Julie’s mum uses are different to what I hear at home – my mum would never say ‘poppet’ – but there are still similar tender words said. The simplicity and tenderness of hearing the adult woman being put to bed by her mother, who just wants the best for her, touched me deeply.

I felt that feeling, of being totally loved. Of someone wanting the best for you, no matter how you behave or even how demonstrative you are back. I felt, too, what the absence of that feels like. Julie’s mother performs the parental role of turning off the lights when her daughter is in bed, asking should she put down the blinds, and then closing the bedroom door. All very calmly and lovingly. But when the door is closed, and she goes into her own room next door, her demeanour takes on a more anxious bent. It is only when she is alone that she can let her true feelings show. A look crosses her face that shows us she is filled with worry for the sleeping girl behind the wall next to her. The burden of being a parent: no matter how hard you try, you will never be able to protect your child from life.

It is a precious thing to be so deeply affected by art that you are moved to tears. Tears that seem to rise up from inside you, deep in the solar plexus, flowing up and up until they reach your waiting tear ducts. It is not silly or trite: it’s beautiful, and we’re lucky to experience it. Sometimes I see a painting or photograph that hits me so hard I feel like exclaiming. It’s like a punch to the gut; an involuntary hit that leaves me momentarily breathless. Sometimes it’s because everything is lined up just so, and is satisfying to see. Or it’s looking at the photographs taken by someone like Vivian Maier or Evelyn Hofer, and seeing beyond the technical beauty and right to the emotions underneath. The humanness of it all.

The beautiful thing is that no two experiences of moments like this are the same. What moves me might not move you. I might sit stone-faced while your insides turn to jelly. I remember watching the Gloaming in the National Concert Hall a few years ago, and during one song the fiddle player Martin Hayes was playing a part where the notes kept rising, higher and higher and higher. It began to sound to me like the keening of a human voice, and my heart swelled in my chest, I willed it to keep going as tears pooled in my eyes. I wanted to cry, to feel the release of the emotions that the music had stirred up in me. In these moments I feel like I’ve been flayed of a protective layer, that all the feelings in me are uncovered and raw.

In The Souvenir, you could read the character of Julie as naive. We look at her privileged life – big house in Norfolk, well-off parents, her lack of interest in discussing the political situation in 1980s Britain – and see a cosseted woman. When I watched her, I saw someone who has been loved so much that she only knows how to love back, so when she meets her terrible boyfriend she is ill-equipped to deal with the consequences of his actions. She sees the world through a lens of truth and integrity, and tells her lecturers in college that in her filmmaking work she is determined to confront her privilege.

But she meets a man who wears a coat of mistruths and concealment and who wears it well. He’s like someone from another time, another era, and his probing questions and seemingly perceptive statements about her give Julie a new way of looking at her world. “You’re very special, Julie,” he tells her at one point. “I don’t think I am,” she responds. He scoffs at this, as though she just does not see things as they really are. She accepts him unquestioningly because she doesn’t know what it’s like to be someone who creates a false exterior. Why, when the real world is there to be embraced instead?

Julie is lucky to be loved, and lucky to love, but we see that she is unlucky too. She lives a life of honesty, and it is that which leaves her most damaged.

The Souvenir is out now.