The stock market is predictable. That is, if one considers human psychology. Some economists miss this completely. For them, the stock market is a confusing, contradictory dynamic that sometimes is very irrational. Hence, just as humans are irrational, the stock market will be irrational as well. Famously, Alan Greenspan said this as an understatement when he referred to “irrational exuberance” just prior to the dot.com mega crash that sent global economies wobbling.
Even more disastrously, in the global collapse of 2008 people had even more irrational behavior. They behaved as though credit was limitless, and what goes up does not necessarily come down. This is just at attributable to laws of physics as the laws of human psychology. What goes up, does come down, sometimes with a whopping crash.
Buy low. Sell high; truer words were never spoken. The trouble is the psychology that drives the market follows trends. If a stock is rising, particularly at a rocket fire pace, people will want to jump on that rocket. They are not going to look at it and note how high it has become. Instead, much more often they will believe that if they get it , then it will go even higher. This is a form of wishful thinking that even many brokers follow for their clients. As to selling low, the reverse is true. If it is going down, this is an opportunity to buy low, but psychology again makes investors fearful. They will panic, quite often, and sell low just to unload the stock.
There are certain predictable trends other than human psychology. Often, some people try to pick stocks according to algorithmic models, numbers games and so on. This can, if done well, put the decision making process into the hands of a computer model, or a Vulcan Spock-like individual who is not affected by either sudden hot rocketing of the stock, or by the fear that drives huge sell offs.
So long as the trading is done without emotion, it is likely to produce much better results. Another factor that not enough investors pay attention to is the fact that they have unconscious views, prejudices, fears and more; these also affect their stock picks. These set up both conscious and unconscious defense mechanisms, such as denial when a person is motivated by perceived gain, and fear, projection and more when motivated by a kind of low level panic. It is safe to say that until people overcome human defense mechanisms, then trading will be predictably unpredictable!