Who said "The hardest opponent is yourself."?

This quote is attributed to Danny Rand.

The hardest opponent is yourself. - Danny Rand

"The hardest opponent is yourself."

Danny Rand

"I am the living weapon. I am Iron Fist."

"My training has taught me that discipline is the foundation of everything."

"I've learned that wealth means nothing without purpose."

"The pain I endured made me stronger than I ever imagined."