The quote "Once a circle missed a wedge" is the beginning of a popular children's book titled "The Missing Piece" written and illustrated by Shel Silverstein. The full first sentence is:

"Once a circle missed a wedge."

This book uses this simple sentence to start a charming tale about a circular character searching for meaning and happiness by seeking out different sized wedges to fill its missing piece. It explores themes of contentment, acceptance, and finding joy in who you are. The story is often used to teach children about self-acceptance and appreciating life's imperfections.