the stock market has a LOT of automated trade. when the price of a highly traded stock falls and reaches certain points it triggers limit orders to buy, and when it rises it triggers limit orders to sell. that's why you never see a clean rising line or falling line for more than a few days at a time, these auto orders run by the huge investment companies always stabilise things a bit. to see larger trends you have to scale up your chart to see past the stabilising periods.