We've all been there. You've just hopped out of your truck for a moment on the hard shoulder to check a map or fertilise the bushes. But you've only gone and forgotten to put the handbrake on, haven't you.
And then there you are, for some reason gripping a big piece of wood, cantering nervously quite some way behind your massive truck as it rolls downhill, chasing the metal beast and praying it doesn't end in disaster.
You watch in horror as it leaves the slip road and freewheels out in front of motorway traffic, crashing into the road's middle barrier. To your utter relief, oncoming traffic stops in time.
Happens all the time! Maybe not. But something very similar did happen to one unlucky guy who was caught on camera by a passing car running after his lorry, in footage posted to Facebook by Mohammed Zahir and viewed over a million times.
"Guardian angles were out in force that day, my goodness!" wrote one Facebook user under the video, saluting the holy acute angles watching over the truck chaser, who brought a whole new meaning to "driverless vehicle".
Others asked why the men in the car didn't help him instead of laughing and filming as the truck rolled steadily towards the motorway, though the driver did start hammering the horn to warn other vehicles as he realised what was about to happen.
Watch the video here, but be warned in case it bothers you: there's some swearing.