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I believe the lore stated in the game is that it is unknown why the seal was broken.

No, it did not. It just simply broke for unknown reasons. As the above stated, that was mentioned in the prologue of Wind Waker. Although, since Wind Waker is based a one-hundred years after the events of Ocarina of Time, the seal may have weakened, since it never stated in the lore whether Ganondorf immediately broke free from his prison. Timelinesplitter 04:12, May 19, 2012 (UTC)