Show, don't tell. That, I was always taught, is the basis of successful writing.
Don't bludgeon people with grand pronouncements, rather take them on a thoughtful journey of discovery which, hopefully, will lead you both to the same conclusion.
In fact, it is a principle that can be applied to almost every aspect of life – from the world of work to parenting.
It's the difference between someone telling you they love you via pointless gestures – and showing they care through constant daily actions, large and small.
It's the difference between politicians who make promises they never keep and those who change policy.
In short, it's empty grandstanding versus industrious authenticity. And, to my mind, it is the ultimate test of a person's character and maturity.
Prince William's Time To Walk podcast is the perfect example.
Everything about it, from the concept to the simplicity and sincerity of its execution – and the fact that Apple is making a six-figure donation to charity on his behalf – reinforces the impression of the Duke of Cambridge as someone who understands the crucial difference between superficial sentiment and meaningful action.
SARAH VINE: There's a wonderful intimacy to his words, a total lack of princely reserve as he talks about his life with charming candour, from his experiences with the Air Ambulance Service to his memories of being driven back to school by his mother, singing along at the top of their voices to Tina Turner. (Pictured: Prince William and Kate Middleton on a walk last January)
A person who gets that you can't just expect people's respect, you earn it.
By showing, not telling those around you (in his case that includes the millions of British citizens who look to the Monarchy for guidance and inspiration) why you deserve your status in life.
And boy, has he succeeded. In just 38 minutes strolling gently through the Norfolk countryside, we learn what so many Royal-watchers have lately come to sense is true of William.
That he is a remarkably well-rounded human being, a man who embodies rather than wears the mantle of Royalty, who harbours an acute understanding of the responsibilities and challenges of his role, who has a real and heartfelt connection to other people.
Someone who recognises his own weaknesses and tries hard to remedy them.
It's clear things haven't always been straightforward for him. We all know the trauma he shares with his brother, of losing his mother at such a young age with the eyes of the world on them.
Yet he is also painfully aware that, compared to the problems of so many others, his own struggles might seem marginal.
And it is precisely because of this self-knowledge that he inspires such empathy. He talks about his experiences of anxiety, of the challenges of his circumstances with such self-effacing sincerity, such honesty, you can't help feel for him.
He doesn't ask for our sympathy; but he gets it nonetheless.
If William's experiences have shaped him into a thoughtful, rather noble individual, poor Harry's seem to have done the opposite, writes Sarah Vine
And that's in large part because there's not a hint of self-pity in what he says. No anger, no desire to lash out or wound. Just a calmness, mercifully devoid of cliches or woke-speak.
There's a wonderful intimacy to his words, a total lack of princely reserve as he talks about his life with charming candour, from his experiences with the Air Ambulance Service to his memories of being driven back to school by his mother, singing along at the top of their voices to Tina Turner.
Interestingly, while he talks about his family and his children, the Duchess of Cambridge is never mentioned by name.
But she doesn't need to be; her influence, the positive impact she's had on his life, is unmistakable.
She is there in the gaps between every syllable, her tacit presence and constant support quietly acknowledged at the end, when he says: 'Feels like I've been on a walk with a best mate, or my wife.'
