Real-life art heists aren't like the movies, and the Rotterdam art thieves won't find collectors for their multimillion dollar loot

A guard looks on at the Kunsthal in Rotterdam, after seven paintings were stolen in an overnight raid. Photograph: Robin Utrecht/EPA

A hundred and one years ago a thief stole the Mona Lisa. On Tuesday morning thieves broke into a Rotterdam museum and grabbed half a dozen masterpieces, including works by Picasso, Monet, Matisse, Gauguin, and Lucian Freud. Together the paintings are worth hundreds of millions of dollars.

Heist movies always focus on how. The thieves scan the layout of security cameras, oil their rifles, synchronise their watches. How is the wrong question. The real question is why.

Why in the world would thieves steal paintings too famous to sell? Plainly, they do. A Museum of the Missing, an imaginary museum that consisted entirely of stolen paintings, would be one of the best and biggest in the world, as splendid and sprawling as the Louvre.

So what are the thieves thinking? Less than you would imagine.

Like the mafia dons who learned proper gangster style from Hollywood, they draw their picture of the high-end art world from movies rather than from life. In a penthouse den with mahogany furnishings, they believe, some modern-day Dr No sits contemplating the blank spot above his fireplace that would make the perfect setting for a Picasso. And wouldn't this unscrupulous billionaire cackle with extra delight at the thought that his new treasure was not only stolen but that no one must ever know its whereabouts?

But there are no such collectors, though the thieves fervently believe in them. Thieves take paintings for the bragging rights, and because they've read the headlines about Van Goghs and Cezannes fetching tens of millions, but mainly because it's easy. Art thieves are no Thomas Crowns. Few have ever ventured into a museum except to rob it. To a thief a painting in a gallery is a million-dollar bill sitting in a frame. Banks hide their treasures in vaults and employ armed guards; museums hang their masterpieces on the wall and hire sleepy retirees to keep an eye on them.

Eternal optimists, thieves reckon that something will turn up. If they can't find a crooked collector, maybe they can work a deal with an owner or an insurance company. If they get only $5m for a painting worth $50m, they can live with that. As thieves see it, art-napping is kidnapping without all the fuss. Here is a victim who won't cry out or jump out the window and who just might bring a giant ransom.

If not, there are always other thieves. In 1990 a Metsu that had been stolen in Dublin four years before turned up in Istanbul, in the hands of a thief trying to barter it for a shipment of heroin.

In reality, nearly all the schemes go bad. Like a dog who finally catches the car he's been chasing, an art thief ends up with a painting he has no use for. So paintings pass from hand to hand, each thief confident at first that he can do what others could not, and eventually learning better. Paintings end up lost or ruined.

Museums, in the meantime, are caught in a bind. Their mission is to put their treasures on display. But to offer the public easy access to great works of art is also to issue an invitation to thieves. There is a limit, besides, to what visitors will put up with. A bird in a plexiglass cage doesn't do much to lift the heart.

In any case, security can only be beefed up so far. If a museum sheaths itself in electronic sensors and alarms during the night, thieves will simply barge through the front doors during the day.

Art theft is that rare game where everyone loses.