It's true, that the children of gods with Epic Dexterity are the masters of the battlefield, normally. But, once in a while, someone is born, who might not be the person most nimble, but who manages to compensate for this with sheer analytical skills and a lot of saavy. He is able to predict enemy movements, use weak points for his advantage and to outmaneuver enemies in a fight.
Scions with this knack may use their automatic success from Epic Intelligence instead of Epic Dexterity when attacking, as well as in computing their defense values. This knack may allow this benefit on some other rolls also, but this depends on decision of your GM. It explicitly does not allow to use Epic Intelligence instead of Epic Dexterity when calculating your movement values - brains are not always a match to superior agility. This knack also can't be used, if the character is sursprised or ambushed.