"I told Bilbo often that such rings were better left unused; but he resented it, and soon got angry. There was little else that I could do. I could not take it from him without doing greater harm, and I had no right to do so anyway."
......

"But why not destroy it, as you say should have been done long ago?" cried Frodo again. "If you had warned me, or even sent me a message, I would have done away with it."
"Would you? How would you do that? Have you ever tried?"
"No. But I suppose one could hammer it or melt it."
"Try!" said Gandalf. "Try now!"

Frodo drew the Ring out of his pocket and looked at it. It now appeared plain and smooth, without mark or device that he could see. The gold looked very fair and pure, and Frodo thought how rich and beautiful was its colour, how perfect was its roundness. It was an admirable thing and altogether precious. When he took it out he had intended to fling it from him into the very hottest part of the fire. But he found now that he could not do so, not without a great struggle. he weighed the Ring in his hand, hesitating, and forcing himself to remember all that Gandalf had told him; and then with an effort of will he made a movement, as if to cast it away - but he found that he had put it back in his pocket.
Gandalf laughed grimly. "You see? Already you too, Frodo, cannot easily let it go, nor will to damage it. And I could not "make" you - except by force, which would break your mind....."