Board Thread:Theories and Speculation/@comment-34656247-20180403003525/@comment-734582-20180405203100

I don't see why Amaterasu should burn everything equally fast to begin with. While Amaterasu burns things inevitably, it was never said that it burns things fast.

Some small objects were burnt easily (Shin's knives), fire burnt easily (Itachi v Sasuke), but large areas can burn for a long time (forests, for instance). the Juubi burnt, but it was also a gargantuan creature. Even if it burnt at the pace of Shin's knives, it would take a long time to be destroyed whole. And the forest Itachi set ablaze was something that burnt on it's own, while Sasuke intently focused on burning Shin's knives.