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.