Unfortunate event like correcting and other stuff that occurs after a huge changes in the market. Bitcoin to 5 USD seems possible but how unimaginable for it to happen. Hitting 6k USD mark is quite tough for bitcoin and in addition it does take time. On the other hand when bitcoin is about to reach that mark it must be completely useless, and unworthy for it not to be worthy of even a single demand in the market which I don't think will happen, and that is the only factor I can imagine of.