Einstein said, "Common sense is the collection of prejudices acquired by age 18."
My mother, a dub in her declining years, told me that common sense could not be learned. She asserted that she had it and that I didn't and that I had "book sense" only. However, I will point out that my life was no more screwed up than hers, and mine was improving while hers was getting worse.
My observation is that when people start talking a lot about "common sense" and claim that others don't have it, if one looks a little closer, he or she will find that the blabberer, most of the time, is a person who has little in the way of skill, education, knowledge or achievement.
I hope your observations and experiences of those who claim to possess "common sense" are better than my own.
Regards,
SandraC