The mechanism of succession to the throne — and particularly the extent to which it can be predicted and/or influenced — is a very important feature of any political system. I want to look at the effects of these features as they apply to hereditary monarchy on the one hand and to democracy on the other.
(Note: For convenience, I will be using the terms king, throne, etc. in the generic sense to refer to the chief executive of a polity. I don’t mean to exclude queens, emperors, presidents, premiers, first citizens, etc.)
In a hereditary monarchy, succession is highly predictable. A potential heir is typically known from birth to be a potential heir, and so his education and pre-coronation career can be arranged so as to prepare him for his future responsibilities. Knowing that he will likely be king someday, he can consciously work to acquire the knowledge, skills, and character traits he will need when it comes his time to take the throne.
In a democracy, no one can ever be very confident that he will be king someday, and certainly not from an early age. Therefore, a new king is very unlikely to have spent much of his life specifically preparing himself for kingship.
In a hereditary monarchy, the order of succession is a given, and there isn’t much you can do to influence it. If you want to be king, there’s not a whole lot you can do to make it happen, short of staging an all-out revolution. If you happen to be a potential heir, you can become king by murdering the sitting king and/or the other potential heirs — but the hereditary system minimizes the temptation to do so by ensuring that the king and the potential heirs are all close blood relatives.
In a democracy, the succession is wide open. In theory, anyone can become king. In practice, you become king by influencing the populace to vote for you, which is best accomplished by developing demagogic skills, cultivating connections with people in power, and (especially in a modern mass-media democracy) acquiring enormous sums of money. These secondary goals are, in turn, most effectively reached by being a complete and utter scoundrel. So that’s what future kings spend their time and effort doing — not preparing to be king, but striving to become king; cultivating not the virtues of a king, but the vices of a politician.
One corollary of this is that in a democracy, the king is always someone who really, really wants to be king, since you can’t attain the throne without trying very hard to do so. In a hereditary monarchy, kingship is the heir’s fate, a duty thrust on him whether he will or nill. Thus, in a monarchy it is at least possible to have a king who is not power-hungry. It’s not at all clear how that might be possible in a democracy.
In a hereditary monarchy, the king serves for life. He cannot predict how long his term in office will last and is therefore motivated to take a long-term view.
In a democracy, the king is typically subject to strict term limits. He can predict with a fair degree of accuracy when his term will end, and he is therefore subject to the temptation to kick difficult problems down the road a few years and leave them for his successor to deal with.
In a hereditary monarchy, potential heirs are the king’s natural allies — both because they are his blood relatives, and because they typically serve in high positions in the reigning king’s government. They are motivated to help the king succeed.
In a democracy, many potential heirs — particularly those not of his “party” — are the king’s natural enemies. Even though many of them also serve in high positions in the government, they nevertheless want the king to fail. Failing that, they want him to seem to the people to have failed. They are motivated to fight against everything the king attempts, to foment discontent among the populace, and to undermine the people’s loyalty to the king and the unity of the polity.