@Tamiel:
I still think Blackbeard and Shanks met before the former joined the Whitebeard pirates. I always pictured that Shanks told him something important, and Blackbeard modified his plan, or made up a plan that would allow him to join Whitebeard crews to further achieve his goals.
Not that it affects anything, I am just trying to figure out whern did he start planning to overtake the seas.
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That's the thing, it is not about him boasting, but him being able to secretly go meet an enemy crew, injure the captain and then lay low. I understand Shanks wouldn't be, they do tend to notice these details. Like when Whitebeard questions him about his arm, and how his battles with Mihawk were heard all over the New World. I am sure neither party was going around talking about it, but somehow the world knew.
Blackbeard always wanted to rule the seas, imo, or well ever since he was young.
He says he went to Whitebeard's crew because he though it would be the easiest way to come across the darkness fruit.
And their fight doesn't need to be a secret, it simply happend more than a decade ago and wasn't that important until recently.
You gotta see a young Shanks and Mihawk like Luffy is right now, a sort of super rookies.
People knew about Shanks' and Mihawk duel like they know about Luffy's involment in the war or the alliance with the Heart Pirates. No one knows that Zoro's carries a scar made by Mihawk because that happened outside the spotlight. No one knows Law beat Vergo.
Whitebeard asks Shanks how come a decent pirate comes back from the East Blue without an arm, what kind of enemy was able to best him. People knew he lost an arm but it wasn't in a major public event so no one knew how, same thing can go for the scar on his face.
Man, we really need that flashback.