Your vehicle breaks down on a high-capacity roadway, such as a highway. After pulling onto the right shoulder, what does the manual say to do?

The stay-inside rule exists because a pedestrian on a highway shoulder is the exact risk it protects against. Walking any distance along that shoulder exposes you to the same fast traffic you pulled off from. This answer frames the stranding as a stuck-and-needs-help problem when the manual frames it as an exposed-to-traffic problem.

The high-capacity procedure is hazards on, seatbelt on, and 911. Standing at the front would put you on the roadway side of the vehicle, right where passing traffic runs. This answer carries over the pre-cellphone habit of raising the hood as a distress signal, from an era before hazards and a 911 call were the expected response.

The high-capacity-road protocol keeps you inside the vehicle. The guardrail step belongs to the lower-capacity list, and even there the manual limits it to when exiting is necessary and safe, from the opposite side of oncoming traffic. This answer reads the guardrail step as universal roadside advice rather than one branch of a road-type split with its own safety condition attached.