I hated being told I should ‘cherish every moment’ of motherhood – now I understand | Rhiannon Lucy Cosslett

Raising a baby is a huge challenge. No wonder many new parents resent the cult of compulsory joy

Of all the phrases parents tell me they dislike, cherish every moment" is the winner. Time is a strange thing when you are caring for small humans, and, as I thought about it this week, it is this phrase that keeps coming back to me. It's the idea that by feeling any negative emotion, you are somehow squandering time. I have been told by parents with postnatal mental health issues that this unrealistic phrase - often said by older people - has made them feel deep shame. Time is precious, and to not feel constantly delighted by your child is a terrible waste.

I don't feel shame, but I'll confess that the occasional suggestion that this column is overly negative has wounded me. I've been writing it in real time these past eight months - I wrote notes for my first column while in hospital, the sounds of women in labour all around me - and though there have been struggles, there have also been immense, intense highs. My son still feels miraculous to me. But writing as it happens means real, living feelings land on the page, some dark, some light. There's no time to try to temper reality in retrospect to make it seem like it's always plain sailing.

When I see new parents out and about with newborns, I feel solidarity but also a strange mix of other emotions. He was once so small and curled like a bug - how could that time have passed so quickly? Why did I not realise how short those days would be? At the time they felt unceasing; in the whirl of feed, sleep, feed, sleep I could not see an end to them. The baby and I were still one, and would cease to be. He would open his eyes to the world and look beyond me, and I would be gifted a whole new phase, while mourning that which came before. At the time, the shock of his premature arrival left little room for reflection - but had you asked me, I'd have maybe said that I felt that the time in the third trimester, when the baby should have still been safe inside me, had been lost, or even stolen. Now I say I got five extra weeks of him. What a gift, this time travel.

When you are raising a child, it isn't that the hard parts aren't hard, but that time marches on so indefatigably that they almost mystically fade. Older people, I think, understand this, which is why they often can't remember when you ask them about specific aspects of parenting, such as my mum not recalling when she moved on from giving me purees, or how they coped with certain difficulties. (In case it sounds as though her memory is going, she just recited TS Eliot to the baby: I have measured out my life with coffee spoons." I could measure the last year of mine in formula scoops, I thought.)

Women have said to me that they suspect this amnesia might be evolutionary, otherwise no one would have a second child. Time makes you sentimental, and pain fades in the memory, with sleeplessness rendering whole stages - where the passing of time felt like treacle - a blur. I'm starting to understand that. The hell of establishing breastfeeding felt, at the time, all consuming. I doubt I'll ever fully forget it, but thinking about it now is like watching a film about someone else, while sitting a great distance from the screen.