If Bitcoin price pumps from $1300 to $3000 in few hours, nobody would make profit from it, because the exchanges wouldn't allow you to sell your Bitcoins and make the fast profit, it would bring a big loss for exchange sites.
Do you agree with this?
Exchanger still make profit from fees. I think one who hold bitcoin will buy dollars when bitcoin is in the peak price, and wait bitcoin to fall again. When the bitcoin is lower they begin to buy bitcoin again. I think only the lucky ones who can predict will gain profit.