Volatility = enemy or a friend?

I'm sure that most of you heard about systems with specific parameters working pretty good for some time, untill they become useless?
So it got me thinking...
Why are some m.a. cross over systems on the d1 perform amazing for some time, only to become completely useless some time afterwards? Which leads the curve fiting. I think I've managed to get an answer why most systems with fixed parameters fail. And the answer is = they don't account for changes in volatility.
It is a proven fact that volatility has changed through out years,months,days on forex.
I suppose the reason for the D1 timeframe is = changes is the interest rates.

So having said that, does anyone even account for volatility ? How would one do that ?

Is that also the reason why fixed risk:reward fails some time after ?

It sounds like you are referring to trade systems. They fail after some time not because of volatility but because of price direction. The market only trends like 30% of the time or so and cross over systems rely on trends. When they are not present, they fail.

The reason why MAs fail after a time is because the market stops trending. And if somebody just takes signals like a machine, he'll lose more during the ranging period, than what he makes during trending.

Same with the tools for ranging environment. They make money while the market moves sideways, and kills the account when it starts to trend.

A good strategy lets you to trade with the trend, and also you can catch reversals with it during ranging. And when the market starts to churn like crazy in the same place, then it keeps you out of the market and doesn't give a signal.

Ok for example a made up example.
Suppose you were trading for 10 years.
10 years ago the average daily volatility was 400 pips.
Through out the years the average daily volatility went down to 95pips.
Now suppose that your system had fixed parameters calculated 10 years ago, moving average settings, stop loss ammount in pips.
Would the changes in volatility affect the performance of your system?

Yeah it would in that case. You would no longer hit your targets as frequently and the system would start losing. That's why I don't like systems. They have to be constantly adjusted for the ever changing market conditions. That's why they will always break at some point.