While for some people, telling left from right is as easy as telling up from down, a significant minority – around one in six people, according to a recent study – struggle with the distinction. Even for those who believe they have no issues, distractions such as ambient noise, or having to answer unrelated questions, can get in the way of making the right choice.

"Nobody has difficulty in saying [something is] front and back, or top and bottom," says Ineke van der Ham, professor of neuropsychology at Leiden University in the Netherlands. But telling left from right is different, she says. "It's because of the symmetry, and because when you turn around, it's the other way around, and that makes it so confusing."

Left-right discrimination is actually quite a complex process, calling upon memory, language, visual and spatial processing, and mental rotation. In fact, researchers are only just beginning to get to the bottom of exactly what's going on in our brains when we do it – and why it's much easier for some people than others.