One series of cases from the Court of Appeal says X. Another line of precedent from the Court of Appeal says Z.
So, today, the Court of Appeal says that the right rule is actually Y. Somewhere between these two competing principles.
Or, in the words of Justice Segal:
"The Kims challenge the trial court’s denial of their motion in limine to exclude
evidence that the custom of the automotive industry was not to include ESC [Electronic Stability Control] as standard
equipment in pickup trucks. In rejecting this challenge, we part company with one line of
cases stating that evidence of industry custom and practice is always inadmissible in a
strict products liability action, and with a recent case suggesting such evidence is always
admissible. Instead, we hold that evidence of industry custom and practice may be
admissible in a strict products liability action, depending on the nature of the evidence
and the purpose for which the proponent seeks to introduce the evidence."
The cases the Court of Appeal cites start twenty and thirty years back. You'd think that if the Court of Appeal was so fractured, the California Supreme Court might want to get on the stick and decide which line of precedent is correct, no?