Who said "A warrior's greatest enemy is often himself."?

This quote is attributed to Shifu.

A warrior's greatest enemy is often himself. - Shifu

"A warrior's greatest enemy is often himself."

Shifu

"There is no secret ingredient. It's just you."

"When will you realize? The more you take, the less you have."

"Your story may not have such a happy beginning, but that does not make you who you are."

"It is said that the Dragon Warrior will bring peace to the Valley."