It is always a good idea to change your strategy based on what the market is doing. This is true no matter how much experience you have in the market.
Bob is the average trader that learned this lesson the hard way. He came into the market during one of the biggest bulls markets ever. He also decided to trade call options because of their huge growth possibilities. After a couple months of paper trading he perfected his system.
Bob now opened an account with $10,000 to trade this new system. Over the course of 2 years he turned this $10,000 into $90,000. Everything is going great, the money is rolling in every month and he feel like the worlds best trader. Then the market crashes. When the market changes his bullish calls buying system no longer works. He was reluctant to change because his system that worked in the past has to work now. But because things are different now he fails to make money.
In fact after 1 year Bob has lost $70,000 trading. He is discouraged that his perfect system failed and pulls his money out thinking if he does he can at least say he came out ahead.
The mistake that Bob made was in thinking that because his system worked in a bulls market it would work in a bears market. It took him losing $70,000 of his previous profit to figure out that wasnt so.
What he should have done was sit on the sidelines and paper trade when the markets changed. If his system still worked on paper maybe he could try betting some real money too. Because his system didnt work he could have tried to develop a bearish system.
That is a common mistake all traders have. The market is always changing and you should be too. It is better to be a cautious trader then a trader who lost all their money.