This summary is not the rule. The rule text controls.
If you're suing the owner of a car under this specific Idaho law, you also have to name the driver as a defendant in the lawsuit, as long as the driver can be found and served with legal papers somewhere in Idaho. This law comes up in cases where the owner isn't the one who was driving, but the law still holds them responsible for what the driver did.
The reason for this rule is fairness. If the driver's mistakes are the reason the owner might have to pay damages, the driver should be part of the case too. This gives everyone a chance to sort out what actually happened and who's responsible, rather than only going after the owner while leaving the driver out of it.
If the driver can be personally served in Idaho, you can't skip adding them to the lawsuit. Only if the driver truly cannot be served in the state does this requirement not apply.
