Immortal prevents your weapon from
breaking, as in being destroyed, ie. - GONE. This can happen when trying to enhance a weapon from +4->+5 and on, although very rare from 4->5.
To stop things from failing to 0, they have to be +4 or higher and have
astral. Astral makes it so when your weapon fails to + it will only be bumped down to +4, instead of +0.
Another useful blue is
Steady, which prevents your weapon from losing durability if it fails (past +4 I think?).
Hope that cleared some things up
