Levels of Abstraction
An expert is able to traverse levels of abstraction and focus on the most adequate level for achieving the desired goals.
Any activity can be broken from high-level abstract concepts to the low-level more tangible components. Let's consider soccer.
The high-level goal is to put the ball into the opponent's goal. To achieve that, in the lowest level, the player must be able to use their feet to kick and handle the ball, besides running, maintaining balance. One level up, a player must be able to pass, kick the ball, block an incoming ball, and so on. Then, one more level up, the player must coordinate with other players, consider the likely advances of the opponent team, consider what passes and kicks to take, and so on. We might even consider one level up where the team considers the optimal strategy in a tournament spaning multiple games.
For a player during a game, it is not useful to think about their feet and neither is useful to consider the overall tournament besides the impact of the current game. The most useful level of abstraction is the tatics and strategy for the current game only.
Of course, at different times it might be worth considering different levels of abstractions. During training, we must drill the control of the ball, passes, kicks. During tournament planning, we must consider the opponent teams that are expected in a tournament. An expert is expected to figure out and focus on the level most suitable for reasoning about the situation.
During a game, a soccer player can't take the time to consciously think about their feet, how they walk and how to manage the ball. There is where chunking comes into effect. Chunking means taking some collection of behaviors and/or concepts, learning each of them in minute detail, but them letting the details vanish from your conscious thought by abstracting them away into a single concept.
In more tangible terms, a player might drill kicking the ball. While practicing that particular aspect of playing soccer. The player is focused in how their control of their feet act on the ball and how out of the expected or desired the trajectory of the ball was. Then the player attempts a correction and tries again, until kicking is drilled down into the unconscious. During a game, the player doesn't need to think about it specifically, since it's “chunked” away into the abstract concept of “kicking”.
Chunking is what allows an expert to abstract away layers of related knowledge which was learned into a single block or “chunk”. It then becomes simpler to understand how a chunk might relate to another, drawing existing and new connections between concepts in a tractable manner.
An expert brings value by being able to make predictions or exercising these predictions during their performace.
Coming back to the soccer player analogy. During a game, a player is always trying to predict what their opponents and also their teammates are going to do. They attempt to also attempt to consider what the opponent team is expecting and attempt to mislead. This all plays into the higher-level concept of tactics or the strategy during the game.
An expert may draw from experience, and thus be able to predict better than their opponents. A player which is able to better predict and react ahead of time is “one step ahead”, and has an edge over another player which is not doing so.
Prediction is precisely the tanginble value that a an expert brings to the table.
A physician will be presented with a situation about the patient, judge what investigations are worth doing and ultimately predict how most likely the scenario will evolve, and what course of action are possible and their predicted outcomes. Likewise, an engineer will be presented with a problem and a set of constraints, attempt to predict the costs and likelyhood of success of different approaches, and present those trade offs for examination.
While doing so, both expert traverse different levels of abstraction, from the high-level goal to the nitty-gritty execution, which is manageable due to how they chunked toghether learned information for considering relevant concepts and discarding unrelated ones, and ultimately producing a judgment or prediction which is valuable for a third-party.