Occult mahjong
Occult mahjong, or flow mahjong, is a school of thought that focuses on luck, instinct, superstition, and the "flow" of luck. For example, an occult style of thought believes that the luck from one hand carries over, or "flows", onto the next.
The converse of occult mahjong is dubbed digital mahjong or "scientific mahjong". A digital mindset focuses on probability and statistics, reading the gamestate first and foremost. Analog mahjong, a more practical form of occult mahjong, focuses on reading the players (e.g. taking an "objectively" worse wait to try and hit a specific player).
History
Mahjong is a gambling game with a high dependence on luck. Therefore, it is natural for superstitions to form.
Before the internet became widespread, occult mahjong was reportedly quite popular (citation needed). Many professionals focused on how to improve your luck. However, in the modern day, digital mahjong is the dominant philosophy.
Occult mahjong takeaways
The use of the term "occult" can be seen as pejorative - saying occult dismisses the entire thing as bogus. It's true that there were many silly superstitions, such as "calling discards to shift the tile luck to you". However, there is an important takeaway: it can be useful to read players. It is possible to gain information by knowing players' habits, behaviors, and/or subconscious cues.
- For a more obvious example, if you know a player tends to discard hatsu after haku/chun, then that is useful.
- Emotions can be read, just like in poker. Players could be visibly excited/anxious when they have a big hand and show it through the behavior, or annoyed when they have a bad hand.
- Trying to read the precise contents of a player's hand, e.g. feeling that a given riichi is a cheap or expensive hand, is in the realm of occult play. However, discard reading as a whole does not count. Basic examples, like "a player discarded a lot of souzu/pinzu, so they are likely to have a manzu honitsu" can be considered basic probability, which is clearly not occult.
These things are hard to reproduce - behaviors change from player and player. Thus, a "purely digital" player may disregard the players themselves, only focusing on the gamestate. The strategy of reading the players may be called analog mahjong, to separate it from the more dubious end of occult mahjong.
Note that an analog play style should be reserved for players with good experience (and thus have a sense of what people act like). New players should focus on digital concepts, like tile efficiency and tile safety. Knowing them is the "baseline" that all players should know, because they can be applied to just about any situation. Also, as you may surmise, an analog style is more useful when playing with physical tiles or with a specific group. In online clients, you'll often encounter a player once and never play them again, and reading emotions is nearly impossible.