Why did Frodo feel he had to leave Middle Earth at the of ROTK?

[Inziladun]

Originally Posted by Lotrelf

Does only the land matter? Trees were killed/destroyed. There was darkness all around, if I remember that correctly. It's like saying poisonous air is not in the land so those who live on the land do not need to fear it, while the birds etc. are in greater danger. It 's a bad analogy, but for now I can't think of something better!

The darkness wasn't permanent, though. It left no lasting damage in the Blessed Realm. I also like radagastly's take, which seems in a more ethereal sense along the lines of where I was aiming.