Well, the other thing about Celtic myth is that Greek tragedy generally unfolds in an understandable manner. Celtic tragedy seems to function by plot fiat. No an outsider, the whole geas thing seems to make no sense. Arbitrary Rule #1! Arbitrary Rule #2! Oh, no, they're in conflict and now you die! Except neither rule made much sense to begin with. It's not like, say, Oedipus Rex, which actually is applicable to personal and civic life-- don't pursue justice at all costs or you may be the one paying it.