Curse

Wasn't get what he or she wants, but wont be able to handle it Mari? You'd think Tarlach would have sorted Ruairi out on all the details he misunderstood or something.

I think Mari is the one who gives up everything since she gave up being a human and her own will to the gods. Tarlach is the one who suffers physical and mental agony for all eternity: this one is pretty easy since he went from having the curse of being a bear during the day, to forcibly aging himself then forcibly regressing his age and his mental state back to a 10 year old, while He has to realize he doesn't have the power to save the erinn and those who inhabit it. Lastly Ruari who gets what he wants but won't be Able to handle it, and this is easy to pin point since Ruari typically wanted power to protect those who was precious to him and the power to defy his destiny. (though we don't know his true destiny is, it could vary from dying or serving under the gods) But we can really understand why he can't handle this power, since even though he gains a lot of power over the generations, it seems he's never been able to master it or truly control it a good , since no matter how much power he gets he's never been able to master it. The easiest way to figure this out is during his roleplay as a dragon knight in g18 how he wields a huge weapon at his size is impressive, but he swings it around like a blunt weapon, slowly and inefficiently, not only that it seems that he hasn't learned a variance in skills besides magic and he forgets basic things like making a campfire. If he had actually used a weapon that was more suited for him he could actually be a more excellent swordsman.