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

This quote is attributed to Lady Sif.

Motivation comes from within; no one can give it to you. - Lady Sif

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

Lady Sif Motivation

"I am a warrior of Asgard, and I will not falter in the face of darkness."

"Strength is not measured by the power of one's blade, but by the resolve of one's heart."

"A true friend stands beside you, not behind you."

"We are forged in battle, but refined through compassion."

"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."