Why is a Princedom acquired by Fortune (define) easy to acquire, but hard to maintain?

New states acquired either by fortune or outside assistance are easy to conquer; the difficulty lies in holding onto power, as Machiavelli argues in his next chapter, “About New States Acquired With Other People’s Arms and By Good Luck.” Here Machiavelli zeroes in on a single protracted example: the story of Cesare Borgia, otherwise known as Duke Valentino, the son of Pope Alexander VI.