Who said "Motivation is seeing someone sad and getting stronger."?

This quote is attributed to Nelson Muntz.

Motivation is seeing someone sad and getting stronger. - Nelson Muntz

"Motivation is seeing someone sad and getting stronger."

Nelson Muntz Motivation

"Ha-ha!"

"Your tears of unfathomable sadness!"

"I'm gonna enjoy this, Bart. I'm gonna enjoy this a lot."

"Eat my shorts, Simpson!"

"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."