Awakening the Past 'Him'
Many things happen while in a breakthrough. It involved both the biological process and a contest of willpower. Unless one had the experience, it was almost impossible to even survive a breakthrough into Tier 2.
"Psychic Ancestor Marble had once stated: In the early days, we didn't know such a concept existed. We called it the expiry date, the time until when a person loses control. Back then, there existed only Tier 1. One day, a person lost control, but he managed to defeat the Wisdom Parasite in him. It was then he pointed at the changes. Eventually down the line, we found the method to initiate a breakthrough. Though, we paid a heavy price to get that data."