Aristocracy as the thermosetting plastic of social positions

The first person in any exalted aristocratic line got there by doing something notable, at least in the eyes of then currently powerful.

But those talented people's children and children's children needn't do something notable to retain that exalted position.

That after all is the whole point of any aristocracy : it is the outward physical expression of a secret mental belief in the sheer randomness of great talent and of the rare chance that a particular great talent will be in perfect sync with the wishes of the contemporary powerful.