User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-4649443-20130607014423

Okay, I think I figured out Piper's Fatal Flaw. And I have to thank Sayu, Solo+pbellUNITE, and every other Piper-hater for giving me the ideas....

So, there's this comment on page 2 of this Discussion where Solo says that Piper only "talks about 'Jason this' and 'Jason that'." also, I remember this old comment where some User thought that she is too whiny about not having any attention from her dad. My conclusion is: Piper's Fatal Flaw=too possessive/obssessive with people.