My five-year-old daughter is having trouble with her friends. Nothing unusual, just the general run of trouble. “X is mean to me and Y. She won’t let us play,” she tells me. “And she said my shoes were dirty.”

X, I need hardly say, is her “best friend”. And, if I remember rightly how this script goes, they probably have in front of them about 20 more years of fighting, making up, small meannesses and quite large betrayals, all interspersed with loving support, till-death-do-us-part loyalty and ferocious cheerleading. Basically, a whirl of make-up-break-up in which they try and work out where they stand in relation to each other and the rest of the world. All things being equal, eventually they will grow out of the tussling, and into all the glories of a strong and dedicated friendship, the kind of thing that makes life – with all its triumphs, unexpected traumas, bad days and small wonders – a better thing.

In my own life, my friends have seen me through a host of troubles, small and large, from problems with childminders to, more recently, cancer. They have also been there to celebrate the good things, making these even better by their presence. They are one of the most reliably wonderful resources I have. And yet, it hasn’t always been like this. The further back these friendships go, and some have roots in early childhood, the more likely it is that there have been rough patches along the way. Moments where we were more in competition than in harmony, determined to outdo each other, be smarter, prettier, wittier, more daring, better paid, more popular, more important.

Youth is a time of arrogance – and rightly so. We all need a strong dose of fairly aggressive self-belief in order to have any faith in our ability to make an impact on the world. We need a few years of thinking we’re the greatest, otherwise we would be far too daunted by the task ahead – simply living – to engage with it. It is also a time of insecurity, of deep wonderings about who we are, how we fit. The two combined can lead to what gets called “bitchiness”; the kinds of interactions between young women that are sparky and a little bit suspicious. That soften with time, but start out faintly hostile.

The best friend who stole your boyfriend, who flirted with the guy she knew you liked; the friend you sneered at behind her back to other friends, mocking her dress sense or way of talking. The friends who “forgot” to invite you to something or ignored you when you got there because they were busy sucking up to someone more popular.

And yes, these are the same friends who sat with you for hours as you wept over a broken relationship, unrequited love, poor exam results, a mean boss or arguments with your mother. Who showed staunch loyalty and belief in you, no matter how much of an idiot you had clearly been.

These are all tableaux from my earlier life, and I suspect they are pretty common. Some of them were also painful: you can’t invest in the notion of friendship without giving that person the power to hurt you. And yet some of the culprits are still my closest friends to this day. These days, we are consistently forces for good in each other’s lives. We are the Greek chorus and cheerleaders, the fair- and foul-weather stalwarts.

So what changes? What moulds the trajectory from bitchy to bestie? It could be Darwinian, biologically-driven – intense early competition for attention, for resources, a mate, giving way to later, softer interactions as we band together to raise children and survive – but actually, I don’t believe that we are quite that led by our most primal instincts. I think we are well able to rationalise them away. Instead, what I think is missing from our early interactions is quite simply experience. An understanding that life is far longer, far more difficult, than we know, and that a great deal of kindness is required to get through. The more we learn this – mostly we have the knowledge forced upon us through difficult life events – the better we understand that the business of living is not a competition, that instead it is a collaboration, one we need to invest in if we are going to thrive.

The only consolation for terrible things happening to us – and sometimes it is scant consolation, but I guess we take what we can get – is that each trauma lived through brings us a little bit more empathy with the traumas of others. If we lose someone close to us, we will forever understand how that feels, and be filled with sympathy for others who suffer in the same way. The same happens with serious illness, redundancy, problems with family, all the many trials that beset us.

There is no such thing as a charmed life. No one gets through unscathed. And so we learn, the hard way, to be kind to each other. To cheer each other on and talk each other down, to share in the ups and downs of each other’s lives. To be good friends in all weather. It may be knowledge hard won, but it’s well worth having.

As for my daughter, I have tried telling her that perhaps X was trying to be helpful in telling her that he shoes were dirty. She’s not having it – “she’s not, she’s mean!” There are some things only time can teach.

The Privileged by Emily Hourican, published by Hachette, is out today, April 14th, and will be reviewed by Sarah Gilmartin in The Irish Times on April 16th