Not necessarily so. Here's where I differ slightly with you, Paul, and with the Pratchet definition. In the eye of the chastiser, that knowledge which is lacking is staring the people right in the face, and yet they are blind to it.
Second, when somebody is chastising another for lack of "common sense" then the tidbit of information that is apparently lacking tends to be something rather obscure.
Jen Fulkerson wrote:I know a person who is exceptionally smart. The kind of person you wonder if there is anything they don't know. In a good and amazed way, not a snotty jealous way. Over the course of our friendship I have offered bits of advice, or a simple solution to a minor problem that got the reaction of course, why didn't I think of that. My inner thought was this person lacks common sense. I have never said it our loud. I certainly didn't mean it in a condescending way, lord knows this person is way smarted then I. My thinking is more that they see things on a different plane, or perception than I, or maybe there brain is so busy working out the complicated, the simple alludes them. I'm on the fence here. If you make this statement to someones face, I think you ether aren't very nice, or need to improve your communication skills. On the other hand I understand this phrase. The common every day things that most of us understand are hard or allude these people, it doesn't make them less in my book, strange enough often they are more. I guess it is how you interpret the the meaning of the phrase, and how you use it