1. Not listening to women is dumb, and sets you up for a world of pain. (Don't ignore the young female druid / seidhkona... you get the picture).

2. Stupidity (and hubris) are equal opportunity. It's Queen Maeve who ignores the warning from the wisewoman Fedelm. It's the men following her who compound it. It's Maeve's husband who insults her enough to make her start the war Fedelm knows will be a blood bath. And it's Cu Chulainn who keeps on going despite the goddess Morrigan placing herself directly in his path and warning him of his violent death.

3. Don't steal from your neighbors, or exploit them. The misery just gets passed around.

and 4. Don't be cocky when you're up against a badass, regardless of how young (or old) they look. Nicely paired with #1.

Also, did I mention not listening to women is dumb? That should be plastered across every cliff notes version of this story, before the antagonist is even discussed. Along with Lugh's teenage avatar learned all his warrior mojo from a lady.

Esoteric symbolism is all about in this epic... like all myths, the stories weren't only on a literal level as entertainment or moralism.. Yes, we know. And all of the above still applies.

For background, see, http://en.wikipedia.org/wiki/The_Tain

For my experiences with Irish deities and myth (including Lugh, who is wonderful), and how to properly honor one of the Irish Goddesses, according to her, see:

Image credit: CĂș Chulainn in battle, from T. W. Rolleston, Myths & Legends of the Celtic Race, 1911; illustration by J. C. Leyendecker. Courtesy of Wikipedia.