Odin, the chief ruler of the gods, was tall and old, wise and reverend. His beard was white and long, and he seemed to be forever brooding deeply over the mysteries of life and death. He had only one eye as he sacrificed the other to obtain great wisdom.

Every morning, Mimer drank a draught with the Gjallar-horn. The then young Odin had deep desire to receive the wisdom and strength which the mead alone can give. He entreated Mimer to give him a draught in exchange for one of his eyes which was cast into the well.He then drank the Gjallar-horn he became worthy to rule over gods and men. Thus Odin taught to all men that self-sacrifice is required to obtain wisdom and power.

This episode is also available as a blog post: http://martinifisher.com/2019/01/25/the-one-big-mistake-deeds-of-odin/