If you can't immediately tell your left from your right without using some kind of trick, you're not alone.
Speaking to Outpatient Surgery magazine earlier this year, Professor John Clarke from Drexel University, Philadelphia, estimated that a fifth of people have the same issue, saying:
Twenty percent of the population has right and left confusion, meaning that they can't immediately tell their right from their left without having to think about it first. That means if I say, "Raise your right hand" to a group of people, 20% might raise their left or have to take a few moments to think about it.
In a study of 1,182 college students, 26% reported having difficulty telling the difference between left and right occasionally, frequently, or all of the time. In a study of 364 university faculty members, 19% reported the same thing.
Either way, it's somewhere around 1 in 5 – and that's a sizable number of people.
If you feel stupid for not being able to tell the difference, don't.
The difficulty stems in part from the fact that the words "left" and "right" are not as self-explanatory as, say, "up" and "down", or "front" and "back".
In his book Right Hand, Left Hand (Orion, 2013), Chris McManus writes:
To decide if one object is above another, we need to know what is 'up' and what is 'down'. That is easy – hold something in the air and let go. The way it falls is 'down' because gravity means things go down and not up. [...] There is nothing obvious in space, such as gravity or the length of our arms, which tells us which way is right and which left. Right and left will, therefore, be harder to use.
Here's a test you can take to work out how much easier you find it to distinguish up and down from left and right.
Even if you think you don't have any issues telling left from right, you'll probably take longer to "read" a picture of left- and right-pointing hands than up- and down-pointing ones.
Typically people can look at the picture on the left and name the way each hand is pointing much quicker than they can the one on the right. Thirty per cent of people who have taken the test online took more than 12 seconds longer to read the left and right hands than the up and down ones.