User blog comment:Masterreaper/What is the Treasure of One Piece?/@comment-3507136-20140616124616/@comment-3507136-20140617130628

Thanks guy, the theory was aimed from the adventure concept of the story. haha, it seems like the most important tool required when sailing the grand line so it sorta fitted haha.

Another theory is that it's that "One Piece" that connects all the other pieces of mystery in the world. Which makes everything make perfect sense, then again, in a flashback, Roger showed it to Whitebeard while sat drinking sake under sakura trees... so it is highly likely it's either pocket sized, OR the cliched, "It's what is in your heart."