Why does the Trigram (or Trigraph) concept use exactly 3 and not 2 or 4+?

Question

Database

Example
https://www.postgresql.org/docs/current/pgtrgm.html
It would be possible to split into 4 characters or more, as well as 2.
Intuition suggests that the point is accuracy, with long or too short pieces, the accuracy drops, but Is it so?

Answer 1

Empirically found the "golden mean". Natural languages ​​are different. For English, with its typical short words, 2 might be fine, but for German, 4+ would probably be better. We experimentally found that on average 3 for different languages ​​gives a good result.