because then he’ll be sacrificing himself to himself.

Erm. Only Odin can do that:

I ween that I hung | on the windy tree,
Hung there for nights full nine;
With the spear I was wounded, | and offered I was
To Othin, myself to myself,
On the tree that none | may ever know
What root beneath it runs.

None made me happy | with loaf or horn,
And there below I looked;
I took up the runes, | shrieking I took them,
And forthwith back I fell.

Nine mighty songs | I got from the son
Of Bolthorn, Bestla's father;
And a drink I got | of the goodly mead
Poured out from Othrörir.

Then began I to thrive, | and wisdom to get,
I grew and well I was;
Each word led me on | to another word,
Each deed to another deed.

Runes shalt thou find, | and fateful signs,
That the king of singers colored,
And the mighty gods have made;
Full strong the signs, | full mighty the signs
That the ruler of gods doth write.

Goes on for a bit with a description of skills attained etc. Havamal, stanzas 146ff. (The stanzas look that odd because Old Norse poetry is nuts and essentially untranslatable)

If you want a boring, materialist interpretation it's a description of a psychological trial caused by the tree of life (the genome), with the result of gaining access to intuitive abilities from precisely there.