It's REALLY not that common
An old proverb says "A handful of common sense is worth a bushel of learning." That just means that your good sense and sound judgment is as valuable as years of formal education. I don't know about you, but sometimes I have to wonder if that is really true or was that just a way to make people feel better about not receiving formal education.
On the other hand, I have encountered plenty of people in my lifetime, no matter where I was or what task I was trying to accomplish, that make me wonder if their formal education is doing them any good. So which one is really worth more?
Actually that's a question that we will probably never really have an answer to. Because common sense is actually based on individual perceptions. Individual meaning single, separate, a particular person and perception meaning the way you think about or understand thus your common sense relies on YOU. We are all different so we are all going to understand differently.
When you are discussing or deciding something of importance don't consider your position or your idea aka your common sense because it just isn't that common! You have no idea what the others around you think or understand, but you do know what they say and do. Make your decisions based on the real, the expressed, the explained and not the "common." If you rely on common sense you will be disappointed by others seeming lack of it 99% of the time.