The Io Instinct is that passion in women which inspires them to consider becoming a part of a love triangle, to steal the romantic interest away from another, and also to feel the pull against such an instinct. On the dark side, her tale offers a lesson that one may never rest when succumbing to the temptation to steal the mate from another. On the positive side, it underlines the power and exhilaration derived from so doing, and finding one's level of seductive power.
Io was a priestess of the Goddess Hera. Zeus noticed Io, a mortal woman, and lusted after her. She initially rejected Zeus' advances, until her father threw her out of his house on the advice of oracles. According to some stories, Zeus then turned Io into a heifer in order to hide her from his wife; others maintain that Hera herself transformed Io.
When Zeus transformed Io, the deception failed, and Hera begged Zeus to give her the heifer as a present, which, having no reason to refuse, he did. Hera then sent Argus, who had 100 eyes, to watch Io and prevent Zeus from visiting her, and so Zeus sent Hermes to distract and eventually slay Argus. According to Ovid, he did so by first lulling him to sleep by playing the panpipes and telling stories. Zeus freed Io, still in the form of a heifer.
In order to exact her revenge, Hera sent a gadfly to sting Io continuously, driving her to wander the world without rest. Io eventually crossed the path between the Propontis and the Black Sea, which thus acquired the name Bosporus (meaning ox passage), where she met Prometheus, who had been chained on Mt. Caucasus by Zeus. Prometheus comforted Io with the information that she would be restored to human form and become the ancestress of the greatest of all heroes, Heracles (Hercules). Io escaped across the Ionian Sea to Egypt, where she was restored to human form by Zeus.