Experts' nebulous decision making can often be modelled with simple decision trees and even decision chains (linked lists). Even when the expert thinks their decision making is more complex, a simple decision tree better models the expert's decision than the rules proposed by the experts themselves.

I've long dismissed decision trees because they seem so ham-fisted compared to regression and distance-based clustering techniques but decision trees are undoubtedly very effective.

See more in chapter seven of the Oxford Handbook of Expertise. It's fascinating!

I once saw a visualization that basically partitioned decisions on a 2D plane. From that perspective, decision trees might just be a fancy word for kD-Trees partitioning the possibility space and attaching an action to the volumes.

Given that assumption, the nebulous decision making could stem from expert's decisions being more nuanced in the granularity of the surface separating 2 distinct actions. It might be a rough technique, but nonetheless it should be able to lead to some pretty good approximations.