'My true will.'
Atticus didn't fully understand why, but he knew for sure that the reason he could withstand all of these wills at the same time was because of his true will.
The wills of another path could never be compared to the true will of one's own. The former was following in the footsteps of another. A false path. It wasn't their true identity, nor was it the path they were supposed to walk.
It was akin to an ant identifying as an elephant and attempting to ram through a tree. The result would be far from what it expected. It would be reality.
This was what played out in Atticus' mindscape. The five wills of the gods he'd killed thrashed around, collectively trying to escape the prison. But no matter how much they tried, Atticus' will didn't so much as flicker.
'The power of true will.'
Atticus had observed that his will was sturdier than the other gods he'd fought in the past.
