It's a recurring scene in desert movies - a group of lost people try to find their way through the dunes but end up walking round in circles.
Now scientists have shown that the old cliché really is true, and that without help from the sun or stars people are unable to walk in a straight line.
Researchers in Germany left six volunteers in a forest and asked them to keep going in the same direction. On cloudy days - with no sun to guide them - the volunteers ended up walking in circles and crossing their paths without realising it.
Clichéd but true: Humans struggle to walk in straight lines without definite points like the sun to guide us
In a second experiment, volunteers were left in the Sahara for several hours with water and food.
Again, they were able to keep to a straight path only when the sun was visible. As soon as it went behind clouds they wandered aimlessly in loops.
Dr Jan Souman, who led the study, said: 'Those stories about people who end up walking around in circles when lost are true.
'People cannot walk in a straight line if they do not have absolute references, such as a tower or a mountain in the distance or the sun or moon, and often end up walking in circles.'
In one part of the study, published in the journal Current Biology, two volunteers were left in the Sahara in southern Tunisia in daylight and told to walk straight. Although neither managed a complete circle, both veered off a straight line.
The study found the idea that we walk in circles because one leg is stronger was untrue
A third volunteer walked at night by the light of the moon. When it was obscured by clouds, he made several turns and ended up heading in the direction he came from.
In another test, six students were taken to a large, flat forest in Bienwald, southern Germany, and told to walk in a straight line.
Four of them walked under a cloudy sky and all ended up walking in circles, despite thinking they were going straight. Two others were able to see the sun - and so kept going in a straight line.
All walkers were tracked with global positioning satellites and their routes were mapped digitally.
Dr Souman, of the Max Planck Institute for Biological Cybernetics in Tubingen, added: 'One explanation offered in the past for walking in circles is that most people have one leg longer or stronger than the other - which would produce a systematic bias in one direction.'
But the researchers disproved that by showing that blindfolded volunteers walked in circles but without any preference for going clockwise or anti-clockwise.
The research is being used to map how the brain uses the senses to guide people.
Ref: dailymail.co.uk