Trading Strategies are not constant , it changes with time. If we think the particular method we were taught in the early stages during trading will still work for the market over time, we may keep on losing because the market changes with time. One particular strategy of trading can't be use all the time.
Even the market behavior is not the same all the time due to economic event, swan event , political/event etc that effects the market, therefore using same trading strategy in trading the changing market over a time without changing your strategy, will definitely put you into incuring some loses in the run, Traders should have various ways of approaching the market and be more of a reactive trader to various market condition than being a predictive trader, this is why some traders loose a lot of money in the market trying to outsmart the market.
This was the reason on why they change a strategy because their old strategy is only set in the old condition of the market and if they keep on using it they will lose because the market isn't the same as the first time they use their start and made a good amount of profits.
A trader can be predictive but they shouldn't remain like that without doing an action. They must also react to the prediction that they have made immediately. Your chance to lose a money will get lessen if you are trying to outsmart the market because you will find different ways on how you can do it. This is better than if you are only chilling and waiting for what the market will throw at you.