In 1503, a Florentine artist took on a commission for a local businessman, Francesco del Giacondo.
It was a painting of his wife, it wasn’t considered anything special.
It wasn’t big: it measured 30" x 21" (between modern sizes A1 and A2).
But about 300 years later, in 1797, it ended up on the wall between much larger pictures in the Louvre in Paris.
The public barely noticed it, until 21 August 1911.
On that day, Vincenzo Peruggia visited the Louvre and hid in a broom closet.
After the museum closed he came out and took the small painting off the wall, it fitted under his coat, so he took it and calmly walked out of the building.
No-one even noticed anything unusual until some time the next day.
Then someone remembered that there used to be a small picture in the gap between those two larger pictures.
No big deal, it must have been removed for cleaning.
Eventually they found it hadn’t, and they realised this was an art theft.
But not just any theft, the thief ignored all the other masterpieces and targeted this painting.
It must be worth more than anything else hanging on the walls.
The newspapers got hold of the story and everyone wanted to know what this masterpiece was that had been targeted above all the others.
The Louvre checked and told them it was known as The Mona Lisa.
The public didn’t remember it, but it was obviously the most valuable painting in the Louvre.
Suddenly everyone wanted to see The Mona Lisa.
They must see the painting that was worth stealing above all others.
But no-one could see it, because it wasn’t there, which made them want to see it more.
The Mona Lisa soon became the most famous painting in the world.
It was as if the Louvre was only half the museum without it.
Eventually, after two years, it was recovered when the thief tried to sell it to the Uffizi gallery in Florence.
It was quickly returned to the Louvre and everyone packed in to see it.
Today, according to director Henri Loyette, six million people visit the Louvre every year just to see The Mona Lisa.
This is known as the scarcity heuristic: people never want something so much as when they can’t have it.
I saw the same thing at the National Gallery’s Caravaggio exhibition.
The star exhibit was the painting Supper at Emmaus: the crowd was seven deep, people had to wait ages to glimpse it for a few seconds.
Yet for the rest of the year it was on permanent display upstairs in the main gallery.
You could look at it all day on your own if you wanted, but no-one even bothered.
The producer, Mike Todd, knew all about the scarcity heuristic.
He had a play running in Manhattan that wasn’t at all successful.
So he hired a lady with arthritic fingers for the box office.
When someone wanted a ticket it took her ages to give them their change.
The people behind them had to wait and this caused a queue.
Seeing the queue, other people joined, figuring it must be a good show.
The queue got longer and people passing decided they couldn’t miss out, so they joined.
Eventually, the queue was around the block.
Todd’s show became a huge success, thanks to the lady with arthritic fingers who unwittingly utilised the scarcity heuristic.
Dave Trott is the author of Creative Blindness and How to Cure It, Creative Mischief, Predatory Thinking and One Plus One Equals Three