Etymonline for: 'exert (adj.)' = 1660s, "thrust forth, push out," from Latin exertus/exsertus, past participle of exerere/exserere "thrust out, put forth," from ex- "out" (see ex-) + serere "attach, join" (see series). Meaning "put into use" is 1680s.
Please help me dig deeper than the definition, which I already understand and so ask NOT about. I heed the Etymological Fallacy, but what are some right ways of interpreting the etymology, to make it feel reasonable and intuitive? In particular,
1. Then how did ex- + serere combine to mean the modern definition? How does it make sense to 'attach or join out' something?
2. I question OED's entry, because it contains the guarding or hedge word
probably, and doesn't answer my question 1 above.