Honestly, did you really think anypony would actually believe that you used to be a mythological Human?

Essentially, any story in which a Human (Or other outsider, like an Elf or sapient dog or somthing) ends up in Equestria, as a Pony or other native, and even after explicitly stating their former nature, nopony will believe them.
This does not include the case where they are Geassed (Mind control, sort of) to not reveal their former Nature. It doen't count if they are afraid of the results so try to hide it, (Although afterwards they might do so after realizing the situation they are in). They have to both try and reveal this and have people dismiss their claims.