The unknown unknown

The following passages from Page 74 of Bauer's book describe the concept of "unknown unknown":

"To make sense of the tension between innovation and conservatism in science, more helpful than the banal distinction between what is known and what is not known is the discrimination of three categories: the known, the known unknown, and the unknown unknown."

"The unknown unknown comprises what we do not even suspect. Indeed, if it were not for history, we would not even believe that the unknown unknown exists."

Bauer mentions this as part of discussing innovation in science. Many discoveries are resisted because they do not fit into the prevailing paradigm; they go beyond the known unknown. Scientists are more comfortable uncovering the details the known unknown.

Bauer claims that this conservatism is not bad, for it is part of the filter that removes mistakes and unjustifiable conclusions and things that are wrong.