So when you sell a stock you are selling to another real person. If you are selling a stock for $110 and no one wants to buy it, then you offer it for $109, then $108, then $107 until finally someone does buy it. The next instant the ticker shows a drop in the price of that stock from $110 to $107. The same could be said when you want to buy a stock. Assume the ticker price is $107 and you decide you want to buy. But no one is willing to sell, then you offer $108, then $109 then ...