I'm sure that everyone has ran trough their heads what could The One Piece be, I also suspect that my idea has also been discussed and someone else already came up with it, but I would still like to share it and see what you think about it, because its the one that makes the most sense to me, considering other shounen anime and their conclusions.
I believe that The One Piece isn't actually something with a physical form, but rather something that not everyone can "acquire", or should i say "achieve", not because they aren't strong enough to reach it, but because they are ineligible to do so. Considering this, my concept of what The One Piece really is is that it's actually all the fond memories of adventures, fun, hardships, time spent with crewmates and other friends. This overall experience "embodies" The One Piece and this really explains what it means to "have it all", to be the strongest, because the true strength, content/happiness comes from within, not from acquiring a devil fruit, money, or an ancient weapon (could be of mass destruction), because those can easily be lost, but the inner being can't be lost just as easily.
So, what do you think of this concept?