Recently I came across a dusty box in the garage that was full of old journals that held all my secrets from 1996.

Rereading them was excruciating, painful even, like hearing a recording of your own voice. Do I (did I) really sound like that? I reread the diaries out of sequence (1999 becomes 2012 becomes 2006) to lessen the shock of a past me unfurling and escaping from the pages like a genie. To be back there so vividly felt like a profound jolt – unnatural even. I had to take it slowly, taking in little bits at a time. Often I didn’t recognise myself. Who was this person who did those wonderful things, who took stupid risks, fretted about things that turned out to be unimportant, loved the wrong people, who had all these feelings?

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But reviewing 23 years of this inner world, some universal lessons (life is short, time goes too quickly, things do get better) emerged.

There is such a thing as a fatal flaw

It doesn’t matter if you are 14 or 24 or 40, everyone has character flaws, blindspots or weaknesses that trip them up again and again and again. The things that trip you up can come in different guises, but underneath is the same old fatal flaw that can dog you for a lifetime (“here shall John always stumble; there shall Jane’s heart always break,” wrote Nabokov in Lolita.)

Years go by and you think the problem is with the city you are living in or the job you have or the thing you want but can’t get. But an aerial view – a plane travelling over the country that is your life (travelling over the years and years and years) – shows a different picture. The fatal flaw was in you all along.

Give me a day and I’ll show you a life

Days are how we spend a life, and while looking back at the big moments can be illuminating, it is the description of the days that will tell you most about what it was like to be you then. But we tend to forget our most ordinary days: what we ate, and who we ate with, what time we got up and the walk to work, the shows watched on television and the books we read. How lovely it is to record some of this ephemera, to look back on happy, eventless days. Rereading them is like that line from Brideshead Revisited: “I should like to bury something precious in every place where I’ve been happy and then, when I’m old and ugly and miserable, I could come back and dig it up and remember.”

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Friends come and go, and that’s OK

Skipping around 23 years of diaries you have an aerial view. Seen from up high, life is a revolving door, with people coming in and out. Very few friendships are not in a state of flux. It’s amazing to see how people that were once so central move off stage, and bit players (a friend’s ex for example or a random workmate) become important later on. Meanwhile, the people who brought you together move off to the side.

Up close, the desertion of a friend can hurt like hell. But as seen from above, across the years, people move close and then away again and it all looks like a dance.

It’s painful to read about your own pain

Diaries are a great cathartic space for you to pour out feelings that may be too raw and ugly for public consumption. You may not believe it at the time, but feelings do fade. To read back over your past self in the grip of big pain is unpleasant. But we forget the texture and minute details of deep emotional and physical pain for a reason. To have a permanent record of the depths of your despair would be to remind yourself of why you should never love or trust again. And we can’t have that so nature gave us forgetting.

You fail a lot – but that’s OK

Looking back, it’s clear any success you enjoy now is built on the fruits of failed labour: the unpublished novels, a 16-part TV series set in a newsroom that never got made, plays that were written but never performed. It’s OK. It doesn’t really matter that those things never took off. They were part of the apprenticeship you realise you had been doing only once it was completed.

Youth is both callow and tender

Only someone very young can boast in their diary about reading Derrida, would describe their 46-year-old parents as “elderly” and then on the next page write a very beautiful poem on the tram about an older woman fumbling with her shopping bags.

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Things level out. You get older and stop trying to impress with the Derrida references, you become friends with your parents, and your gift for poetry leaves you mysteriously when you turn 25.

The past is another country – they do things differently there

In the diaries people tell you they are late because their watch has stopped, they smoked in restaurants and clubs, they buy packets of ciggies with loose change. There are references to dropping film to develop at the chemist, long tracts of the early diaries were written in cafes waiting for people who may or may not turn up (they couldn’t text you, you never really knew where anyone was), there were parties that were never photographed that now exist only as recollections of pen on paper.

Time barrels forward, always, and in its momentum we forget the small details of the past.

• Brigid Delaney is a Guardian Australia columnist