etymology is cool.

from "www.etymonline.com":

jack-in-the-box

1570, originally a name for a sharp or cheat, "who deceived tradesmen by substituting empty boxes for others full of money" [Robert Nares, "A Glossary of Words, Phrases, Names, and Allusions," London, 1905]. As a type of toy, it is attested from 1702.

jade (1)

"gemstone," 1598, from Fr. le jade, error for earlier l'ejade, from Sp. piedra de (la) ijada (1569), "stone of colic, pain in the side" (jade was thought to cure this), from V.L. *iliata, from L. ilia (pl.) "flanks, kidney area."

jade (2)

"worn-out horse," c.1386, possibly from O.N. jalda "mare," from Finno-Ugric (cf. Mordvin al'd'a "mare"). As a term of abuse for a woman, it dates from 1560. Jaded "dulled by continual indulgence" is from 1631.

consider the phrase, "beating a dead horse," and you possibly approximate the 1386 meaning of "jade". as it originally referred to a mare, perhaps the transference to the more current meaning ("dulled by continual indulgence") was not too much of a stretch.

also, interestingly enough, jade (gemstone) could have also been an indirect reference to fatigue; kidney or flank pain may be considered symptomatic of certain forms of indulgence. that applying the gemstone to the area in question was thought to be a remedy could be another way that we arrive at the current meaning of "jaded."