Who said "Motivation comes from within—no one can give it to you."?

This quote is attributed to Captain America.

Motivation comes from within—no one can give it to you. - Captain America

"Motivation comes from within—no one can give it to you."

Captain America Motivation

"I can do this all day."

"When I first arrived at Camp Lehigh, I was just a scrawny kid from Brooklyn. But I learned that being a soldier isn't about size or strength."

"There are men laying down their lives. I got no right to do any less than them."

"I'm just a kid from Brooklyn. I can't do this."

"I believe in working hard for what you want."

"Never underestimate the power of determination."

"I don't need a reason to fight."

"The most important thing is the mission. Nothing else matters."