[the phantom]

Where are you getting this that Feanor is mentally weak, Sauce? That's one of those things that always gets thrown around about him because it sounds good. But in reality, from what I've read, he was rather strong mentally.

Are you saying he was weak because he was influenced by Melkor? That's hardly good reasoning. That's like saying the strongest man in the world is physically weak because he can't lift a mountain.

The two trees were the most amazing of the Valar's works, so Melkor resolved to destroy them. The Silmarils were the most amazing of the Elves' works, so Melkor resolved to steal them. Feanor was the most amazing Elf, so Melkor resolved to mar him. It's as simple as that. Only the Valar could have prevented Melkor from achieving his goals. Only they had the power.

But instead of hindering Melkor, they helped him by giving Feanor a punishment (temporary banishment from Tuna) that, as Tolkien said, made the lies of Melkor appear to be true. Given the fact that the only beings powerful enough to undo Melkor's lies instead increased them, is it any wonder Feanor remained stained by Melkor, and that his father's death at Melkor's hands and the theft of his treasure pushed him over the edge?

The circumstances of Feanor's fall were extreme. His fall was the result of a precise series of awful events orchestrated (in Melkor's case) or at least not stopped (in the Valar's case) by beings with greater power than his own. And the fact is, Feanor's fall had to happen in such a way, because he was not weak willed or weak minded. Only events exactly as they happened could have broken him.