This is for the collectors among us. (it's pretty obvious why dealers sell).
I thought for a bit of fun, I'd post a survey about why collectors sell. I'm sure many of us could choose multiple items, so just choose the one that best fits. Feel free to post a reply to elaborate on your response.
I'll start thing off, I mostly sell my dupes. Sometimes I buy a big lot especially when starting new set. So I tend to sell the dupes that I accumulate. But the idea of a mosuleum is kind of tempting.