In the Grail/Arthurian mythos, the Fisher King is wounded and presides over a land stripped of vitality, lying sick or lame in a sumptuous castle slowly falling into ruin. The castle of the Fisher King features a strange passage of time, as if decoupled from the normal flow of time. Maybe the theme of time refers to the events taking place in some privileged state, somewhere between the normal world and the world of archetypes. Maybe this refers to a sort of nodal point or point of renewal of a cycle.
In accordance with the heroic archetype, Percival is expected to bring new life to the land and heal the ailing king by passing a test. The test consists of questing for and finally being revealed the Graal and asking the apparition 'whence it cometh and whom thereof was served.'
Percival is so awestruck by the apparition that he forgets all and the land is not healed. This will only come later.
We could say that Percival failed to self-remember. We could also say that Percival was awed by effects and forgot the duality inherent in spiritual matters, 'whom thereof is served,' i.e. the difference between the polarities of STO and STS. Of course such discernment is only meaningful if one is consciously present in the first place, i.e. remembers oneself.
As many characters of the Grail mythos, the Fisher King may be a composite. The French word pecheur may mean either sinner or fisher. The king may be sickly or wounded, often in the thigh, as a result of some sin of the king. The Cassiopaea material associates the theme of the wounded thigh with being a representative or puppet of higher negative forces. In this light the hero's work of restoration has to do with discernment and promoting free will. Whom is thereof served?
An additional difficulty of interpretation comes from the fact that the 'good' and 'bad' elements and forces and symbols may be swapped in the retelling. Still, we retain the central theme of asking to discern and thereby reviving the ailing world.