Who said "I've learned that the hardest battles are internal."?

This quote is attributed to Arrow.

I've learned that the hardest battles are internal. - Arrow

"I've learned that the hardest battles are internal."

Arrow Strength

"My name is Oliver Queen. After five years in hell, I have come home with only one goal: to save my city."

"I'm not the man I was."

"You have failed this city."

"I'm a monster."

"Strength comes from within."

"A woman should be proud of who she is."

"A strong woman can overcome anything."

"The only thing I'm good at is killing."