What is the difference between a slip and mistake?

Brain Food

There are two ways to think about errors that people make. Some occur when people don’t know what to do because they haven’t learned or been taught to use something properly. These are what we call mistakes.  Some examples of these are sitting and waiting for table service at a pub where you are supposed to order at the bar. Another is trying to use an old Xbox game controller like a motion-sensitive Wiimote and gesturing with it in the air when you need to press the buttons. For a particularly amusing example of a potentially embarrassing mistake, have a look at the story of Rob’s car journey.

Others occur when people do know what to do, in fact that may have successfully done this thing before many times, but they still make an error. These errors are called slips. Examples include leaving your change in a chocolate vending machine or forgetting to replace the petrol cap after filling up your car with fuel. Or even accidentally typing a wrong word when you’re writing a text, even though you know how to spell it, sometimes you’ll still type it wrnogly. To understand a little more about slips, have a read over Stacey’s railway station bathroom story.

The difference between slips and mistakes is important. If someone makes a mistake because they don’t know what to do, we can train them to improve their performance (for instance, someone telling you in the first example that you have to order at the bar). But training doesn’t make us any less likely to slip up.

On error diary, we collect instances of both types of error. For instance, error #1330 is a particularly sweet example of a mistake where toddlers put their wellies on before their trousers because they haven’t quite learnt how you are supposed to get dressed yet. In time, when the children have grown up a bit, they will (hopefully) stop making this mistake. There are also plenty of slip errors on the site, for instance our colleague, Dom, struggled to type his name recently, going with “Dim” instead. Despite typing his name many thousands of times in the past, he typed it wrongly in this instance. It wasn’t that he’d forgotten how to type it, no training was required, it was just a simple slip of the finger.

“Too cute #errordiary: Toddlers in girlfriend’s nursery will put on wellies before trousers as they haven’t learnt to dress properly yet” – #errordiary #1330

So it looks as though we can’t do anything about slip errors, they can’t be prevented through training so perhaps they are just inevitable and unavoidable! Perhaps we should just give up?

No, of course not! That wouldn’t be very interesting, would it? Good design can come to the rescue and help to prevent the unintended consequences of slip errors. Take for example, cases of unmanned drones crashing. In the ArsTechnica article, the author talks about the design of the controls used to fly drones. In one instance, an operator who was ready to land a drone reached out to press the button to release the landing gear on the drone, only the operator over stretched, and hit a nearby button. This button was the ignition button, and therefore the operator cut the power to the engine and instead of bringing the drone to a controlled landing, the drone, now without power and without a landing gear, crashed to the ground.

We know that humans will make slips, and so we can design in a way that makes the consequences of slip errors less irreversible. This is the reason that many emergency buttons will have a safety casing, so that if someone physically slips, they can’t accidentally press that big red button! We can also add extra steps to make sure users know exactly what they’re doing, how many times have you gone to close a document when that little window pops up asking if you want to save it? Without that window, you might have closed the document and lost all your hard work.

If you found this interesting, maybe you’d like to take a look at some of the other stories and articles in our Learning Zone?