Here's something new I've been thinking about:
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I understand why Mara appeared before Ben just to send him off in the correct direction for his investigation. Force ghosts only appear when circumstances really call for them (such as Obi-Wan telling Luke where to go in ESB, Anakin Solo appearing in Traitor to direct Jacen). So why did Mara appear before Luke? Well, to comfort him. If that's true, why doesn't/hasn't Anakin Solo appeared to comfort Tahiri? Why has he let her become just as pathetic of a Sith as Jacen? I don't know if this is an author thing or character thing but it doesn't add up to me
"Changes are nice--but so is continuity!"
"Then you saved my life. How disgusting. How unfortunate."
"No, don't gush on so. It was nothing, really."