[wildwood]

Urgency is the answer. If a stock trades 50K shares today, there had to be a buyer and a seller for every share. If the buyers have the urgency, the stock will rise; if the sellers have the urgency the stock will decline. If for example alot of the public wants to sell stock and there are not enough buyers, then that is where the specialists on the floor of the exchange pick up the slack and "make a market". That is their function, but they only do this at prices favorable to them. The specialist will buy the stock everyone wants to sell, but only at lower and lower prices to reduce their risk. The specialist will then try to sell the stock into a rise later on. (Reverse this process if there is an imbalance of buy orders).