Manwe's Naivete

Creatures lose indestructible and can't have or gain indestructible.
But he did not understand evil, even in the form of his own brother. He released Melkor from Mandos, thus allowing him to cause the distrust of Feanor, the Poisoning of the Two Trees, the murder of Finwe, the theft of the Silmarils, and the revolt of the Noldor.