Divine_Wino says "Because kings are appointed through heredity there is no need to be dissapointed when they turn out to be bad leaders or horny or corrupt."
Actually, kings and queens are not necessarily "appointed through heredity" -- several countries have had elected kings (Poland is the only one I could name off the top of my head, but liveforever tells me Denmark had an elected monarchy until the 17th century) and in cases where the monarchy is normally hereditary, there have still been instances where there was no biological heir (or too many) and someone else had to be selected, either by the monarch before their death (as with Elizabeth I selecting James I) or by other leaders within the country (the English selecting the Protestant daughters of James II to rule, rather than his Catholic son). Vongrim adds, "You could add Malaysia which has a few sultans who rotate being head of state between them. The election is among them (sort of how cardinals elect the pope). The term is 5 years."