Arthur Conan Doyle's fictional character "Sherlock Holmes" is based on his real-life professor under whom he studied medicine,Dr. Joseph Bell.
"It is most certainly to you that I owe Sherlock Holmes and though in the stories I have the advantage
An example that Conan Doyle gave in his memoirs:
Dr. Bell: "Well my man, you've served in the army"
Patient: "Aye, Sir"
B: "Not long discharged?"
P: "No, Sir"
B: "A highland regiment?"
P: "Aye, sir"
B: "A non-comissioned officer"
P: "Aye, Sir"
B: "Stationed at Barbados"
P: "Aye, Sir"
...
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To his audience of Watsons it all seemed very miraculous until it was explained, and then it was simple enough.
That it is not good observational skills alone that make someone "able to read people like open books" and making correct inferences takes a lot more than just that.