The term 'Expert' is used to describe "one who has acquired special skill in or knowledge of a particular subject through professional training and practical experience" (Webster's, 1976: 800).
The association of experts of a field with the "special" abilities deemed necessary to achieve expertise is often misconstrued. Such associations are perhaps made by newbies, who see the task as manifold and thus, mastery is superhuman.
However, the expertise of the expert lies in the domain and is often not extended to its rational counterparts (Memory of chess players -- Djakow, Petrowski and Rudik 1927). The superhuman nature of experts can be attributed to the tacit knowledge acquired by exposure to instruction and extended practice that simplifies the manifold implicitly (unconsciously - without much/any thought from the conscious self), leaving the higher level decisions (low dimensional) to the explicit cognition.
Defined as the kind of knowledge that is difficult to transfer to another person by articulation, tacit knowledge is often learnt implicit and can be attributed to the pattern perceiving nature of the human mind. Instruction or professional coaching help target, build and exercise tacit knowledge -- perhaps by exposing the learner through an optimal environment in which an individual is most likely to acquire the knowledge and (or) help in better organisation of the acquired (example, by the regulating the order in which knowledge is acquired). It also, restricts the manifold in which a newbie might wander, trying to pick up tacit knowledge into a simpler detail, thus saving on a lot on practice.
The nativistic approach of innateness of expertise might only be true in that the physical ability necessary for is inherited. However, the individual should go through the whole of training to achieve expertise. An interesting drawback of tacit learning lies in the learning of annoying habits (against expertise) with equal ease and probability (another reason for the presence of an instructor). In such a case, one needs to train to unlearn the same.