Rezo has met a great deal of people during his life, and that includes troublesome 'perfect' individuals. Still, the statement throws him off because Rezo has never thought of his desire to cure himself as seeking perfection.

"Do you think perfection is unattainable for humans?" Rezo asks. "I do, but... One can always seek improvement."

Especially if that improvement is just to get you to the level of a normal person.