How to infer someone's occupation

How to determine a person's occupation. I think any friends who are interested in detective reasoning may have already tried similar attempts—for example, standing idly on a bus and judging the occupations of the people around, or sitting leisurely at a café by the roadside, watching people come and go, and thinking about their possible professions.

Friends who have read the part "A Study in Scarlet" in Arthur Conan Doyle's "Sherlock Holmes" may remember this passage:

"A logician does not need to have seen or heard of the Atlantic or Niagara; he can deduce from a single drop of water that it may exist, so life as a whole is a huge chain, and by seeing one link in it, one can infer the state of the entire chain. The science of deduction and analysis, like other crafts, can only be mastered through long-term and patient study; even if people devote their entire lives, they may not reach the pinnacle. Beginners, before attempting to study the extremely difficult matter of the mind and the psychological aspect of things, might as well start by mastering simpler problems. For instance, when encountering a person, one should immediately try to identify this person's history and occupation. Such exercises may seem childish or boring, but they can sharpen one's observational skills and teach people where and what to observe. One can tell a person's occupation clearly from any of the following: their fingernails, sleeves, boots, the knees of their trousers, the callus between thumb and forefinger, expressions, shirt cuffs, and so on. If combining these observations still does not make the investigator suddenly realize the truth, that would be almost unimaginable."

This passage is one that Watson found exaggerated and boring in the article, but in the novel, it is exactly what Mr. Holmes wrote. To show his contempt for the article's author, Watson said, 'Lock the author in a third-class carriage, make him guess everyone's occupation, and gamble at 1 to 1000 odds.' And in the following part of the novel, Holmes used his observation and analysis to demonstrate that he initially knew Watson came from Afghanistan and even further deduced that a postal clerk delivering letters used to be a navy sergeant.

"Not so."The moment I saw you, I knew you were from Afghanistan. Due to long-standing habit, a series of thoughts flashed through my mind like a gust of wind, so when I reached a conclusion, I didn't even notice the steps I had taken to get there. However, there were indeed definite steps involved. In your case, my reasoning process went like this:
'This gentleman carries the demeanor of a medical professional, yet has the bearing of a soldier. Clearly, he must be a military doctor. He has just returned from the tropics, as indicated by his dark complexion; however, judging by the contrast of the dark and light skin on his wrist, this is not his natural skin color. His face looks haggard, which clearly shows that he has recently recovered from a prolonged illness and endured hardship. His left arm has been injured and is still somewhat stiff and inconvenient when moving. Now tell me, where could a British military doctor have gone through hardship in tropical regions and suffered an arm injury? Naturally, only in Afghanistan.' This whole series of thoughts took less than a second, which is why I blurted out that you had come from Afghanistan, and you were quite surprised at the time.' 'Understanding this is relatively easy, but explaining how I understood it is not so simple. If you wanted me to prove that two plus two equals four, you'd naturally find it somewhat difficult, yet you know it is an indisputable fact. Across the street, I saw that this man had a large blue anchor tattooed on the back of his hand, which is characteristic of sailors. Moreover, his manners reflected the traits of a soldier, and he had a soldier-style beard; hence, we can say he is a marine. His attitude is somewhat arrogant and commanding. You must have noticed his posture, head held high and waving a cane, right? From his appearance, he seems to be a steady and dignified middle-aged man—so based on these observations, I believe he once held the rank of sergeant.'
Although the analyses above, taken from several passages in the original text, could only be applied at that particular moment, it also shows that judging a person's profession through observation is not impossible, although the success rate is not as infallible as that of Sherlock Holmes in novels. Here, I think that to truly do this well, the process requires the following two steps:
Daily Observation and Verification:
One must try to seize every opportunity in everyday life to observe, but what should one observe?I remember seeing a friend write the following points to observe here, and I personally think they are worth considering.\ 1: Hands. This is similar to many forms of physiognomy where you start by looking at the hands. Certain details on the hand can indicate a person's possible profession and background. Conan Doyle also pointed out a few aspects: nails, and calluses between the thumb and index finger. Regarding nails, this usually refers to their length and any substances remaining in the nail crevices. For example, if white powder is found under the nails, combined with clothing or other characteristics, one can boldly hypothesize that this person works in education; the white powder is chalk residue. Of course, generally speaking, educators in traditional schools also tend to have some white powder on their pant legs or sleeves. Another example involves nails — for instance, yesterday when I went to the Australian immigration office to renew my visa, I took the opportunity to carefully observe the officer. I noticed that most fingers on the right and left hands had nails, except the right middle finger and left index finger which were quite clean. This can indicate that the person has a habit of biting their nails. In Australia, people with this habit usually work in reception, and their reception work is generally labor-intensive.\ 2: Appearance, such as face, waist, hips, and feet. During the Kangxi era, Shi Lang, nicknamed "Sea Thunderbolt," once suggested while training the navy: "Northern people are good at horses, so they have big hips; we Southerners are good with water, so what feature do we have? Large feet. Large feet help maintain balance on the deck and prevent dizziness."\ 3: Clothing. Conan Doyle mentioned "sleeves, boots, and the knee area of trousers, as well as shirt cuffs," which follows the same idea. Usually, one can infer a person's occupation based on how clean or dirty these areas are, or their wrinkling. Here, we can extend Conan Doyle's 'boots' to include shoes, following the same principle.\ 4: Speech and behavior, meaning a person's way of speaking and their temperament. This is intrinsic and cannot be easily changed. For example, in "The Sign of the Four," there is mention of having a military temperament. What exactly constitutes a military temperament can really only be tacitly understood and not literally explained.\ Of course, mere observation is not enough; it is important to accumulate experience over time.The following describes some characteristics that certain professions might have, mainly including habitual clothing (excluding special outfits worn for particular events), habitual actions, and physical traits. Here, expressions and facial appearances, which are more abstract, are largely not considered. Additionally, what is mentioned here are general phenomena, and special cases are not excluded.

Teachers in old-style schools (except physical education teachers): White powder residue in the fingernail grooves, and white powder in the folds of sleeves and trouser legs. They are quite likely to be talkative.

Chefs: Poor facial skin, slightly overweight, generally strong wrists; the arms and backs of their hands used for heavy labor may have small burns, and their hair may smell of oil smoke.

Receptionists (unclear for domestic cases, more complicated; abroad, in some busy areas, mainly those at government offices or the tourism industry for external reception): Tend to bite their nails, relatively wide hips.

Old-style train drivers: The sole of the right shoe wears out significantly more than the left, and facial skin is poor.

Taxi drivers: Long-term taxi drivers generally have varying degrees of stomach and spinal issues.

Freight truck drivers: Spinal issues are relatively prominent, hips relatively wide, body shape varies with location and can involve varying degrees of overweight, poor facial skin, calluses on the inside of the thumb and index finger.

Surgeons: There is a diagonal mark on the upper inner side of the index finger, said to result from frequent use of surgical sutures.

Carpenters and masons: When smoking, they tend to hold the cigarette in their mouth for long periods, so generally, cigarette butts are very short and filled with saliva.

Clerical workers who frequently use pens: Knuckles of the index and middle fingers are prominent.

Soldiers: Generally eat quickly, walk quickly, are more introverted, not good at talking, and tend to be obedient.

When shaking hands, if the other person's fingers feel particularly long and strong, it may indicate considerable artistic talent, such as good handwriting, painting, or piano playing.

Swimmers: Regardless of gender, shoulders are especially broad, upper body roughly forming an inverted triangle; meanwhile, athletes playing Australian football have less broad shoulders and more proportionate bodies; soccer players' leg muscles are particularly developed; gymnasts are generally not very tall.Table tennis players tend to have slightly hunched backs... If it's someone who plays musical instruments, those with thicker fingers often play plucked instruments, such as the guzheng, konghou, or harp, because some pieces require a certain amount of force to play. People with long fingers and a large span (especially between the thumb and index finger) play keyboard instruments, as some pieces require pressing keys across an octave simultaneously. As for those who play string instruments, such as the erhu, violin, viola, and cello, the pads of the left-hand index, middle, and ring fingers develop calluses from being rubbed on the strings.