You pity her. You see her, you speak with her for a few minutes, learn about the myriad of tragedies in her life (and there's always something new), and you just feel bad for her. You want to help. Really, it's easy for Rarity to let somepony stay with her for a little while, just until that guest truly gets back on their hooves, because the mare needs help.
You pity her. And when the pity runs out... that's where the self-loathing starts to come in.
(Part of the Triptych Continuum, which has its own TVTropes page and FIMFiction group. New members and trope edits welcome.)
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