[Mithadan]

Another point is that while Bilbo and Sam "possessed" the Ring, neither "claimed" it, at least while having knowledge of what it was. Sam "borrowed" it but resisted the temptation to claim it. Bilbo considered the Ring to be his own, but without knowledge of what it was or its power, and even so had difficulty relinquishing it. Even Frodo did not "claim" the Ring until he stood at the Cracks of Doom. In contrast, Isildur had, at least, some idea of what it was and by considering it "weregild," actually claimed it. While this is a weakness on the part of Isildur, it may have played into his refusal to destroy it. Having claimed the Ring, it was beyond Isildur's power to destroy it.