Basically, the 'Efficient Market Hypothesis' and Newtonian physics are both wrong. Markets don't accurately price things to 1/100th of a percent every second thought the day. Stocks go up and down though random chance and bubbles are all too common. A more basic failing of the efficient market hypothesis is the lack of a standard level of risk tolerance. However, as a general rule it is vary hard to significantly beat the market over time and for most real world objects F = M * A.