The fifth stage of Mana Foundation, the Neural Stage, was the first major hurdle that a person faced on their journey as a Magus.
All the stages before this could be considered to be relatively easier.
Mana first nourished the person's skin, then their flesh, their bones, and finally their organs. All the organs were thoroughly washed by mana except one - the brain!
In the Neural Stage, mana had to seep in through the organs and then strengthen the nervous system. This was a very crucial stage because the brain also needed to be elevated by mana.
This was a highly delicate process and any small mistake could lead to devastating consequences.
The potion that Adam had brewed, Purple Twilight, and the frosty liquid that he had prepared combined the attributes of fire and ice and permeated every inch of his skin, creating pathways and allowing the mana to flow through smoothly.