Q. Recently, I've been seeing a lot more of my older sister – we have small children the same age, and we are also involved together in organising a ruby wedding party for our parents. We usually get on quite well, and I do love her, but she's driving me mad. She's always been a high-achiever, and she's quite competitive.

I'm doing my best to pull my weight with the party, but she checks everything I do, and often overrides my decisions, which I find hurtful and undermining. She gets very stressed, saying there's so much to do, but won't let me take parts of it over for her, even though I have more time than she does. She won't let me look after her children (aged 13 months and three years), who have a strict routine – only home-made food, no sugar, no screens etc.

She admits she's a perfectionist and being with her makes me feel inadequate – about parenting and everything else I do – though I'm usually confident. What can I do?

A. People often mistake the meaning of perfectionism. It can be more of an affliction than an asset, despite the boasts of candidates on The Apprentice. Satisfaction perpetually eludes perfectionists, as they constantly fall short of the impossibly high standards they set for themselves. For all the practical benefits of efficiency and order, their lives are blighted by a Sisyphean futility. So the first thing you need to remember is that being your sister is probably more painful than being with her.

Yet their zealous ways, however unhinged, are often enabled or applauded by others. My first boyfriend had a much older sister, whose cleanliness and exemplary housekeeping made her the apple of her mother's eye. When I finally went to visit her gleaming home, everything around her was indeed spotless and organised. But privately, she confessed to me that her obsession with keeping everything perfect made her life hell. She changed her underwear several times a day and was terrified that visitors would bring germs into her house on their shoes. Most of us hadn't heard of obsessive compulsive disorder back then (though now the term OCD is slapped on anyone who's a little uptight, or even tidy), but I do hope that poor woman got some help.

That's the extreme end of the spectrum. But the problem is that perfectionists do somehow get to occupy the moral high ground. Their way is the right way, because it is thorough and, invariably, done by the book. In comparison, you feel scatty. Yet that is to overlook all the other elements that make for creative work – and good parenting: instinct, messy emotion, risk-taking and imagination. These qualities are less quantifiable, but they matter too. You need to have the confidence to value your own talents and attributes.

Your sister is a bit of a control freak, and you will probably never care about the flower arrangements and RSVPs as much as she does. Perhaps there's not much point in both of you losing sleep over it. You've done your best to pull your weight. If she's unwilling to concede any of her burden to you, leave her to indulge in the perverse pleasures of martyrdom.

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