Odin hanged himself from a tree for nine days and nine nights, and pierced himself with a spear. He also ripped out his own eye.
It seems they're both equally "metal".
Why did he do that to himself?
He hanged himself to obtain the secret of the runes, so basically to learn magic. His eye was given away for a sip from Mimir's well, the Well of Urd, at the roots of Yggdrasil, which gave Odin cosmic knowledge and wisdom.
Those are good reasons. I'd do that to learn magic and know everything.
Norse mythology points to the sacrifice being necessary to learn magic runes. As an obsessor of knowledge, in particular anything that could somehow help him to survive Ragnarok, Odin does a lot of things that are in the pursuit of that.
Obligatory shoutout to the anime Vinland Saga, which explores the Christianization of viking culture as one of its main themes, and has an absurd amount of effort on display in terms of historical accuracy.
Extra shoutout to the book The Long Ships by Frans G Bengtsson, an amazing adventure comedy around the christianization of the Vikings.
It's a bit melodramatic at times and most characters don't look their age, but the live action series The Last Kingdom explores similar topics with a fair bit of attention to accuracy.
