Common sense is stuff that should be obvious to a reasonably bright adult
I don't think being "bright" has anything to do with it. I have encountered many people who would not be described as "bright" with oodles more common sense, than some of the brighter people I have encountered. Common sense is good sense and sound judgement in practical matters (the basic level of practical knowledge and judgement that we all need to help us live in a reasonable and safe way). I once had a very bright neighbour with 3 Engineering degrees, who asked me to drive him 30 miles because his wife had locked herself out of the car and the engine was still running. I told he to tell her to stick a potato up the exhaust. He couldn't work out why!