Old knowledge is a burden that hampers your performance

If you are trading based on Technical Analysis, using a trading strategy that is statistically profitable, then you need to adhere to the signals of that system. High knowledge of the past, as well as fear of doing wrong, is increasing the risk of letting irrelevant things affect your trading:

	You might for example get a buy signal from a bottom fishing system that you do not dare to follow since you learned a lot of bad things about that company lately.
	You might have a favorite stock, one you trust to climb often, and you buy from the signal you expect to get instead of waiting for the signal.
	You might ignore to buy at stock that you already have had a bad transaction in, although you know that your trading system signals a sound trade.

Old knowledge also throws you out of the trades to early:

You are in a profitable trade and is "talked out" of the profit that rightfully belongs to you.

Old knowledge hampers your performance, you need a strategy for profits to take off

The professional fund manager will be surrounded by knowledge of the type above, and others that will confront them with such knowledge. An active trader will also build a lot of similar knowledge. It is necessary to form strategies that helps you to avoid the pitfalls of that knowledge. These strategies not only need to tell you when to buy or sell, but also what to buy or sell. Many people are focusing on when, but are you aware that the "what" is also a very important question for a strategy to define?

There are many strategies that work in the market, and if they fit your personality, you can use them for profitable trading. But if you do not follow those strategies, the combination of those strategies combined with your cherry-picking may well turn your trades into losing trades. There are many different lines to use to cross to the profitable side, but they are all thin and will break if you burden them with unnecessary cargo.

Old trading systems are like old knowledge, they might hamper your performance

Do you know if your trading system was ever profitable? That it is still profitable? Or are you using a system some "expert" told you works? Or something that is tested and optimized in such a way that it might be over fitted? However you trade, you better test that the basis for your trading is sound.