Who said "The mind grows only when challenged."?

This quote is attributed to Missandei.

The mind grows only when challenged. - Missandei

"The mind grows only when challenged."

Missandei Education

"I am Missandei of Naath, interpreter and advisor to the Dragon Queen."

"Daenerys Targaryen chose to free us, not because she needed us, but because it was right."

"Knowledge is power, but wisdom is knowing how to use it."

"I have served many masters, but I chose to serve the Mother of Dragons."

"Education opens doors."

"Education opens doors to endless possibilities."

"I ain't got the education you got, bub."

"You can't put a price on history."