Last night, I headed to a restaurant after work with my sister to celebrate our parents' 30th wedding anniversary.
On the way, I dashed briefly into a shop, bought a novelty card and scrawled a hilarious (in my own opinion) message, thanking them for begetting two such incredibly excellent daughters; because when it comes to my family, public gatherings are usually the source of mirth and mischief, rather than anything particularly sentimental.
The evening, though, took a course I wasn't really expecting.
After the aperitifs, my mum pulled out of her handbag a written note - a letter she'd penned to dad the night before, that she intended to read out loud at the table.
In the letter, she chronicled all the myriad reasons why, on paper, they were utterly wrong for each other, doomed from the outset by seemingly irreconcilable differences.
She's an eternal optimist and he likes to muse on the gloomier aspects of life, she likes to have friends around her all of the time and he often prefers misanthropy, she walks way too fast and he walks too slow, and so on.
Following this though, she read aloud a list of all the reasons she's grateful for the thirty years they've spent together.
She thanked him for his smiles that convey more than words, for making London her home, for his 'you've only got one shot, make it count' take on life and for giving her the two daughters that she can't imagine living without.
Dad, sticking to his usual laconicism, didn't say very much, but reached for her hand across the table and gave one of the smiles she'd written about.
And for a few minutes, it felt like the restaurant had melted away around us.
So what is it about expressing gratitude that is so powerful?
Over the last couple of years, thousands of column inches have been given over to the value of the phrase 'thank you' in relationships - the suggestion being that these sorts of affirmations can counteract the build up of negativity that leads to divorce.
Save of course for those seriously dysfunctional partnerships - those that house psychological warfare or even physical violence - more often than not, a lack of communication is the source of the problem.
Of the 468 people studied by UGA's Centre for Family Research, most cited 'demands' and 'withdrawal' in communication as part of the relationship break down.
So, to extrapolate, we're either not communicating enough or, when we are, we're communicating the bad stuff and making demands.
I'd have been (and so would you) forgiven for thinking that my mum's letter to my dad was just a nice little gesture she'd dreamt up on the eve of their anniversary.
It turns out, however, that it is a very particular tool, used by psychologists all over the world, as a means of positively reinforcing relationships, romantically but also in other circumstances too, such as between friends and bosses and employees.
UC Berkeley's Greater Good Science Centre explains: 'Feeling gratitude can improve health and happiness; expressing gratitude also strengthens relationships.'
'Sometimes,' however, 'expressions of thanks can be fleeting and superficial. [The exercise of writing a gratitude letter] encourages you to express gratitude in a thoughtful, deliberate way by writing—and, ideally, delivering—a letter of gratitude to a person you have never properly thanked. '
They also state: 'Research suggests that while there are benefits simply to writing the letter, you reap significantly greater benefits from delivering and reading it in person.'
So that explains why she whipped the note out at the dinner table.
Huh, good one mum.
Carrot and Stick
The most wonderful thing about this expression of thanks is just what a powerful antidote it is.
Looking at the various research on the subject, it appears that one thoughtful gratitude letter might be able to counteract months of withdrawal and not-so-positive behaviour.
What this proves is that once again, the carrot has much more agency than the stick.
So, it's probably time to dream up some 'thank you's, now you know that love doesn't always speak louder than words.