Purple

Jack took his seat on the plane, happy to find an attractive man in the next seat, who introduced himself as Trevor. After some pleasant chatting, Trevor asked, “What's your greatest fear?” Jack thought before answering, “I guess, not existing. Like, not mattering.” Trevor pulled a purple box from his pocket and said, “If you could put all the good in your life into this, how heavy would it be?”

“Not very.”

“No. It would weigh the same. You can't quantify good, or a life. Everyone matters.”

“What's actually in the box?”

“You. I'm collecting characters for my next book.”