Common sense is the problem because it can't be defined.
Some years ago I use to make ink mixers, just like a food mixer on steroids. The idea was they mixed printing ink in the tub it was despatched in to save cleaning out mixing tubs. This stuff is horrible the lightest smear of this stuff on your hands and Gert has purple knickers for a month.
So we had to get these things past CE and H&S and RFI and British Nuclear fuels etc, etc
To this end we had the help of the Derbyshire Small Industries Board who were very, very helpful, probably as we were paying them ?
Guy comes round and we talk the whole operation thru, when it comes to guarding the paddle in the ink tub which revolves at from 200 to 800 rpm he asked why stops you putting your hand it.
I replied common sense as no way do you want to come into contact with this stuff. His reply was, as you cannot define common sense and it means different things to different people you cannot use the phrase in the handbook.
At this point we broke off and went into the house for a brew. That morning I had been down to Argos and purchased a new kettle as I'd worn the old one out, so brand new kettle on the work surface complete with shiny new CE certificate. So filled the kettle with cold water and called across, "Look at this " and put my hand inside the kettle. "Look I've 'burnt myself" then proceeded to pour the cold water over my hand "Look burnt myself again" and nothing in the kettles handbook about sticking my hand inside a boiling kettle or pouring boiling water over my hand. Just generic warning to be careful.
Point taken says he signing off a future wave of knicker staining machines