There are few things as strong as shipping containers, it's true, but if not used correctly there can be serious issues. The photo shows a badly loaded container ship where the bottom containers have collapsed causing the whole stack to topple over.
And this is not rare at all. The MV Rena (below) lost an estimated 900 containers when it ran aground, broke up, and later sank off the coast of New Zealand in October 2011.
Photo courtesy Maritime New Zealand
The reason why the stacks in the picture above are still intact but leaning over is because containers lock together. They are also lashed together using steel lashing rods. These will eventually break apart as the ship breaks up and sinks. Despite the container locks and lashing rods many containers are still lost at sea.
The world shipping council puts the average number of containers simply lost at sea over the last years as 546 per year. If you count catastrophic events the number of shipping containers lost at sea goes up to 1,679 containers per annum (2008 to 2013). The numbers are increasing along with the increase in overall global trade.
Containers stack up to 12 high and each container can be holding 30,000 kgs so the stresses are considerable. Back down to earth for storage usage it is also important to remember that if you cut a door or a window out of a container without adding supports you will lose strength. Many trucking companies refuse to transport containers with panels removed or cut outs as the loss of integrity of the form could cause the container to collapse.