Common sense should not be defined as common knowledge. It is not describing a type of knowledge which one simply know or ignorant. Rather it describes a most general type of critical thinking process where common people will reach the similar conclusion when they are asked to engage in the critical thinking.

For example, cutting vegetables. I would say it is a common sense to always put your holding figures on top (rather than under the vegetables or on the side). It is not a common knowledge -- for one, not all or quite a portion of our population never cut vegetables before so it can't be a common knowledge; and for two, many who try to cut vegetables will make mistakes of injuring their fingers due to lack this common sense.

However, it is a good example of common sense, if we imagine, that we ask any common people to think about the situation and devise or choose from a couple vegetable holding position, most of will reach the common conclusions.

Therefore, common sense is a common critical thinking process shared by us.

The problem with common sense is that most people -- or many of us most of the time -- do not engage in critical thinking, as a result, fail to benefit from common sense.