Picture a row of dominoes: one push starts a chain, and every domino that falls belongs to that same chain. A proximate cause is the cause that sets off a natural, unbroken sequence of events producing the loss, with no new, independent cause stepping in along the way.

Example: a driver carelessly hits a utility pole. The pole falls on a parked car, and the downed wires start a fire that burns a shed. The driver's carelessness is the proximate cause of both the car damage and the shed damage. The fire came last, but being last does not make it the legal cause, because the fire was itself a result of the crash.

Efficient proximate cause is the version used in property insurance when a covered peril and an excluded peril combine to produce one loss. In California it means the predominant, or most important, cause of the loss, and the loss is covered only if that predominant cause is a covered risk. Insurance Code §530 ties the insurer's liability to the insured peril being the proximate cause, not a remote cause.

Timing alone does not decide it. The California Supreme Court warned against reading efficient proximate cause as simply the first or triggering cause (Garvey v. State Farm, quoted in CACI No. 2306).