In your opinion what are the reasons that let someone start dumping his bitcoins and walk away ?
I personally (and this is just my opinion) that it's more panic then simply his need of money or something else , as we saw on the BitcoinXT last time , people started to panic and simply sold their bitcoins and that caused a drop in the price .
Simply because they are afraid to incur more losses. So they just withdraw it to stop losing money. For me, I didn't consider it as loss when the price is decreasing not until I totally withdraw it or convert from Bitcoin to local currency. When the price is decreasing we are only incurring a paper loss so don't get panic immediately. Bitcoin is too big to lose so we can never go wrong if we will just hold it for a while.