When my son Julian was three years old, I signed him up for a group music class.

It was a popular programme at a reputable Japanese music school - the same one I'd attended nursery and kindergarten at, and where I'd taken weekly piano lessons well into my teens. As we waited for the class to start, munching on kaya toast at a nearby coffee shop, I filled Julian in on what to expect. He listened and nodded excitedly.

We held hands, skipping to the music studio. "Yay!" we chanted. "Music class! Music class!"

Then, once in class, he froze and turned sullen.

He refused to join the other kids in the songs and movements. He refused to clap out the beats under the teacher's encouragement. He refused to go forward to collect stickers.

It was as though someone had swopped sons with me the moment I crossed the studio's threshold.

"I don't get it," I told my husband when we filed out after the session. Julian was right as rain; completely cured of his sudden-onset petrification. He remained tight-lipped when I asked him what had come over him but asked to go back for another lesson. Yet, when the next lesson rolled around, his bizarre metamorphosis from boy to statue happened again. And again.

"I don't understand," I repeated, shaking my head. "I don't understand him."

It has been a refrain in the seven years since. Toddler or pre-teen, Julian is often an enigma to me. I have since realised that his behaviour often follows a logic generated by his deep and intense personality. I doubt my son - a seasoned choirboy who performed a few months ago at a Kagoshima youth arts festival - remembers his odd musical debut all those years ago, but I finally recognise what I, as a borderline-exhibitionist extrovert, failed to then: stage fright and shyness. What I took for capriciousness had merely been an acute attack of self-consciousness.

Still, each day brings new instances in which I fail to "get" my first-born child. His declared dislike of all animals except turtles (taking him to the zoo is torture). His preference for 1950s-style polo T-shirts in sombre colours (I finally wised up and let him buy his own clothes). His hatred of 3D movies (I love them).

The thing is, I find my younger son Lucien, seven, as easy to read as an open book. He's straightforward, communicative and sociable, like me. We are eccentrics, always up for impromptu late-night karaoke sessions. He is comfortable articulating his feelings: "I cried from happiness at the end of Fantastic Beasts And Where To Find Them, when everything got fixed", as opposed to the monosyllabic grunts I get from his brother. Unlike Julian, who began forming strong opinions early in life, Lucien is pliable. He can be persuaded to accompany me for hours on plant-buying sprees, stoically fending off mosquitoes on orchid farms and displaying polite interest.

Yet, reading over the list I'd written of my seemingly effortless rapport with Lucien, I can see how flimsy it is. I can think of a million counter-reasons, and examples of when Julian and I had shared an affinity.

"You know," my husband has said more than once, "he is just like you."

Until he upgraded it recently, Julian had a mobile phone with wonky facial-recognition technology. The phone unlocked only when it scanned his face. But, sometimes, if I held my face at a certain angle, it mistook me for him and unlocked, too. The resemblance extends well beyond the physical. My bull-headedness - my rebelliousness and easily bored nature, my teenage eye rolls and tendency to question every perceived injustice - is reflected in the face of this young man I raised. We share the same stubbornness: in him, it ends up frustrating and confounding me. His anger, which flashes hot and quick, is so like mine. His anxiety and neuroses match the ones I have.

Like like poles on two magnets, our similarities repel each other. My inability to understand my child is ultimately denial; partial blindness - a refusal to accept myself fully, warts and all.

Perhaps, it is not my older son that I do not "get", but parenting the first child that I struggle with. Like that three-year-old from years ago who had received a verbal picture of music class from an enthusiastic adult, I approach each phase in my 10-year-old son's life with a rosy, hazy idea of what to expect, only to be stupefied by reality when it happens.

Instead of complaining that "I don't understand him", I could simply reframe it as a matter of "I don't understand how I should react": A quick, quiet confession which lifts a burden and defuses a bomb.

"It's easy to take sides and announce 'I love my children equally' or confess 'I think I love one more'," wrote The New York Times' parenting blogger Lisa Belkin back in 2011, about the debate over whether all parents have a favourite child. "What's hard is accepting that relationships are fluid, determined by the ever-changing variables that make a child (and a parent) who they are at any given moment. Those ups and downs, imbalances and inequities, are not something to overcome, but rather realities to be accepted."

I will always work to check my blind spots when it comes to Julian. And given that they are both such distinct and loveable personalities, the way I relate to and parent each of my sons will have to be different.

If anything, I am clear now on which boy occasionally needs that extra bit of affection and reassurance I can give: The unfathomable one who risks being ignored or misconstrued by the hectic world - in all its cruelty and inattentiveness - will always need a safe harbour and a listening ear.

•Clara Chow is the author of Dream Storeys and co-founder of art and literary journal WeAreAWebsite.com.