Who said "Sometimes I think I'm the loneliest person in the world."?

This quote is attributed to Charlie Brown.

Sometimes I think I'm the loneliest person in the world. - Charlie Brown

"Sometimes I think I'm the loneliest person in the world."

Charlie Brown Solitude

"Good grief!"

"I got a rock."

"Rats! I did it again."

"Why is it that everything I do turns into a disaster?"

"Sometimes being the best means being the loneliest."

"Solitude gives us time to reflect on what matters"

"I'm not good with people, never have been."

"I feel like I'm disappearing."