Tacit knowledge refers to the knowledge that is present in the mind but without the consciousness of the subject. Subject doesn’t know the presence of tacit knowledge. It is difficult to transfer tacit knowledge from one person to another by means of language. Explicit knowledge is the knowledge within the scope of consciousness. As opposed to tacit knowledge, explicit knowledge can often be expressed in language and transferred by either writing or verbalizing it.
Expert is a person who has acquired certain special skill which is generally not found in average human being. Expertise refers to the mechanisms responsible for superiority while applying that particular skill.
Erricson and Lehman (1996) argue that experts don’t differ from average beings in terms of their basic capabilities including IQ and their superiority is very domain-specific. They tend to perform equally in other domains. This has been demonstrated among chess players by Djakow, Petrowski and Rudik (1927). Same idea is supported by Taylor (1975) is his experiments with artists and scientists. The superiority of expert in domain increases with experience and knowledge attained, especially by deliberate practice in that particular domain (Erricson, Krampe, and Tesch-Romer 1193). However, when Groot (1978) instructed renowned chess players to think aloud, they did not differ from other people. Reber, in his book, states that people are unable to justify their decisions sole on the basis of consciousness (Nisbett and Ross, 1980). In decision-making, something other than explicit information is required. We can conclude that knowledge gained by experience is important and residual of knowledge is not in the conscious but tacit. Maybe, either residual of knowledge is so weak to be in conscious or that knowledge has been expressed in other representation which is not comprehensible by conscious (In general, the knowledge expressible only in form of language is comprehensible by conscious). Hence, the residual of knowledge in implicit memory plays role while making decisions.
Above discussion supports the role of tacit knowledge in expertise. How exactly tacit knowledge affects expert’s decision-making process is open research question. Erricson states that representation of knowledge in expert is different that enables him to adapt easily and improve performance. Maybe this representation (other than language) of knowledge resides in unconscious part of mind.