Why do we need a trading system?

[AyushPrem]

If you are an active trader and not making money on the stock market, it is time for you to slow down and think about what you did wrong and investigate on the trading system that you are using.
Building a profitable trading system requires time and patient. One trading system may work for some people, but fail for others. It is ok if a trading system fails on you, but it is not ok for you to move on to the next system without investigate it and find out why it doesn’t work.
There is no trading system that will work forever. You will need to adjust or change a trading system under different economic circumferences. If a trading system consistently worked for you in the past and it is not working anymore, it is time to investigate it.

[SamuraiTrader]

A trading system is needed because one must have rules to define behaviour in trading. The trading environment is chaotic, with unlimited possibilities and decision points. Without a plan to define the markets this will likely overwhelm the trader and cause them to make poor decisions and ultimately lose their account. The human brain likes some degree of order. A trading plan and system provides it.