Frodo did not destroy the Ring; Gollum did. This is something he would always be reminded of, especially since the very finger that bore the Ring was missing. In the end Frodo had failed. His will was not strong enough to complete the deed. However, it is doubtful if anyone else could have completed it either. The great King Isildur had failed in the same spot at the Cracks of Doom. No one else had even attempted it, nor were they willing to try; only Frodo had the courage to carry the burden to the fire. For lacking the strength to throw it in we should forgive him.