The value of a stock is based on the overall markets prediction of how that company will perform. If you can predict how the value of a stock will change, you a

The value of a stock is based on the overall markets prediction of how that company will perform. If you can predict how the value of a stock will change, you are not predicting how the company will perform, but are predicting how the company will perform relative to the overall market's prediction. That market has a lot of very smart people spending a lot of time making their predictions. If you can consistently identify stocks that are undervalued then either you are smarter than the rest of the market, or you know something the rest of the market doesn't. It is possible to be smarter than the rest of the market. Particularly if you are investing in relatively low value companies and doing significant due diligence yourself. However, if you work in Congress, it is much more likely that you got your edge by knowing something that the rest of the market doesn't, and we have generally decided that it is illegal to make trades based on that information.