Relief Efforts

On the way to pick herbs, Ed made sure not to lose out on his assimilation skill for a second longer. He assimilated a tree, well, a tree branch.

[Vitality +2]

[Constitution +2]

[Assimilation has leveled up]

And to his surprise, it leveled up! Ed couldn't even remember when the last level up had occurred, it became plainly obvious that assimilation did not affect itself, as disappointing as that was.

'It could also be that I need to start assimilating more exotic items' Assimilating the same things over and over again yielded less experience. 

Ed had discovered such was the case for assessment previously deduction, and it also likely applied to assimilation. It wouldn't be too farfetched for the skill to eventually reach a standstill given that was likely the case.