In a hereditary monarchy, the king rules until he dies, or abdicates in favor of his son. If this breaks down, through war, sibling rivalry, or lack of an heir... that tends to be a real problem.

In the United States, the titular head of state is chosen through a weird gameshow, and any given head of state can play that game twice. On two occasions, the son of a successful game show contestant has leveraged name recognition to also win a round in the hot seat.