Who said "Motivation comes from inside, not from other people."?

This quote is attributed to Kenny McCormick.

Motivation comes from inside, not from other people. - Kenny McCormick

"Motivation comes from inside, not from other people."

Kenny McCormick Motivation

"Mmph mmph mrmph!"

"I'm not fat, I'm just big boned"

"Dude, we're in third grade"

"This is so cool"

"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."