I am pretty sure the condition for successful following is actually Fae Blessing, as I hit the wall without it and made it through with it [1], both of those without changing my skills (with Fae Sight and without Fae Step).
(also, it would be very annoying if you could block yourself from completing this quest by choosing to be fae sided, then completing Lost Son for any other reward than fae step)
[1] first tried to talk to the fairy (didn't work), then danced with it, then talked to it (worked)
and any day after that, I just danced first, then talked (and it worked)