Chances are you're always going to have to adapt to changing market conditions - regardless of the underlying 'fixed' trading approach that you may have formulated.
The word "adapting" does not mean changing and moving onto other new approaches, it means using your same approach and understanding what parameters it happens to perform on successfully - such as various market cycles & volatility readings.
I can say with certainty that a fixed black and white trading system will not be profitable all the time, and it will wipe out an account given enough time. It has to adapt to underlying market sentiment.
The issue is that Market Sentiment, and understand this fully is totally separate to technical analysis and creating a system. Market Sentiment is an area of study that is not really talked about in great detail, it's also not an obvious thought process. After many years of trading, learning and developing technical trading systems I now always put Market Sentiment before settling on the variables that will go into a trading system.
To put this in plain English lets imagine your design a Formula 1 racing car, built for racing tracks that are flat, clean and well designed [this is the trading system that you have developed]. The racing car performs well when it's on the race track, but now the race track changes to an off road dirt track [this is the same as the market]. Now your Formula 1 racing car is not performing so well...
You see, markets change in cycles - so you need to adapt to the various sentiments [or race tracks in the above example]. Have your dirt tires, chassis and suspension ready, you can still keep the underlying engine - just like you can keep using the fundamentals to a well designed trading system. But you need to be ready to change variables when required. This is adaptation in its true sense.