This is easy for me I am a Chessmaster and the reason for this is that those that use their instincts to trade the markets can be really effective but it is impossible to determine if what you are doing is effective in the long term because you cannot really backtest your strategy at all because your previous knowledge about the market will affect how you react to it, so the only way to test if you are an effective trader is by using live results and that can take a long time.

But if you instead use a set of strict rules about what to do and what not to do depending on the circumstances then you can backtest your strategy and you will be able to tell very quickly if what you are doing is profitable or not.