Who said "Gratitude is the solution to the riddle of discontent"?

This quote is attributed to Riddler.

Gratitude is the solution to the riddle of discontent - Riddler

"Gratitude is the solution to the riddle of discontent"

Riddler Gratitude

"Riddles are the most honest form of communication - they demand truth wrapped in mystery."

"A mind that cannot solve a puzzle is a mind that cannot live."

"Questions are the doorway to knowledge, answers are merely the threshold."

"The greatest riddle is why people fear enlightenment."

"Gratitude makes life richer."

"A grateful heart is a happy heart."

"Respect those who came before us."

"Life's greatest treasures are the people we love"