I have experienced this several time and I don't know why it happens that way. I think it is a coincidence because the value I do sell sometime are insignificant to create any changes in bitcoin pricing.  we should hold more than selling as this is what stregthen Bitcoin and its market. A time is come were we would be mostly use bitcoin to purchase goods and pay for services and by then we would only concern ourselves with it purchase power and not the returned we get buy holding it. I believe in this future and that is why I will keep holding the major part of my Bitcoin for long terms .