It depends solely on who you ask, the beginning.
Will shall tell you it was the draw and pull of the sea, and the open opportunity to just jump in head first and take what was coming for him, although prompting him properly might make him admit that Jack, perhaps, had something to do with it.
Ask Mr. Gibbs and he'll get that forlorn look in his eyes, right before he launches on a story about a blacksmith turning pirate to be with his one true love. It goes on and on, but you can't leave. Not without hearing what happened, not before buying the man a drink, since all that talking certainly makes his mouth dry.
A certain pirate captain is rather tight-lipped about the matter, though he does get this longing look on his face until his eyes meet Will's.
When the look is returned, it is more often than not that they both melt in a smile, scurrying over to be closer one another, and that, ladies and gentlemen, just might be the true beginning. The feel of belonging, the need to never let go. A pull that's stronger than the sea's.
Mr. Gibbs sits back and brings forth undead pirates, gloating on how his savvy Captain handled the situation, and this is the part people don't believe, even when it's the truest of them all.
Two people know that they're bound by blood. Accidentally, for that matter.
Whether the bloodbond matters or not, in secret, both the men believe it's what will help them through thick and thin.
Some heard stories of Jack Sparrow having been clubbed over the head, so that he simply doesn't know what he's doing anymore. His heart disagrees.
But, then again, there is a rumour, that all the stories are true.