Who said "Isolation is the key to his strength."?

This quote is attributed to Graff.

Isolation is the key to his strength. - Graff

"Isolation is the key to his strength."

Graff

Character in Ender's Game

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"A commander's most important job is to give orders that can be obeyed."

"Humanity does not ask us to be happy. It merely asks us to be brilliant on its behalf."

"He's too much a leader already."

"You are the hope of humanity."