[new2628]

At least in chess, if it is not the search, then it is probably the evaluation function.

Expert players have likely a very well-tuned evaluation function of how strong a board "feels". Some of it is explainable easily: center domination, diagonal bishop, connected pawn structure, rook supporting pawn from behind, others are more elaborate, come with experience and harder to verbalize.

When expert players play against computers, the limitation of their evaluation function becomes visible. Some board may feel strong, but you are missing some corner case that the minmax search observes and exploits.

[YeGoblynQueenne]

I like to caution against taking concepts from computer science and AI and applying them directly to the way the human mind works. Unless we know that a player is applying a specific evaluation function (e.g. because they tell us, or because they vocalise their thought process etc) then even suggesting that "players have an evaluation function" is extrapolating far from what it is safe. For one thing- what does a "function" look like in the human mind?

Whatever human minds do, computing is only a very general metaphor for it and it's very risky to assume we understand anything about our mind just because we understand our computers.