Nothing is as it seems in Grimms' Fairy Tales. A frog might be a prince; an old hag might be your next BFF; and you'd better watch where you take a leak in the woods. You know, in case one of the trees turns out to be someone under an enchantment. Characters in these tales are constantly undergoing transformations, sometimes literal, and sometimes in terms of internal state (becoming mature) or social status (becoming stinking rich). Hence the message to be nice to everyone no matter who or what they seem to be, since that fish you wanna eat might be an enchanted prince…or just a talking fish. Neither of which really sounds that appetizing.
Being transformed into something/someone new is a necessary occurrence in all fairy tales.
Transformations follow gendered patterns. As in, men get transformed into more Xs and women get transformed into more Ys.