Curse

Like I said, "get what he or she wants but won't be able to handle it" is neither Ruairi nor Tarlach, since they never did get what they wanted. Mari, on the other hand, was dying to know the truth of her birth and parents (and funny enough it literally happened) and had trauma over her, which is why she refuses to speak about her past.

We don't exactly know all the details of what Tarlach told Ruairi. The only thing we get is that Tarlach told Ruairi that there's a possibility of resurrecting Triona using Lia Fail, and their past conversations just stop right there.