Regarding the lifetime of a trading strategy

Hey guys, talking in terms of position trading :-
I have read all over the Internet that our strategy will lose our edge over a period of time but when you read books by Andreas clenow (stocks on the move etc) he preaches to follow the strategy for a long period of time(20 years) . Andreas says that our strategy will outperform the index if we do it for a long period of time.
This seems to be true to some extent, I have backtested a simple moving average crossover. Over a period of twenty years the cagr is pretty impressive(25%, though the volatility is high and we probably have deep drawdowns around 20-30%) but still if a simple strategy as this can give 25+ returns over a long period of time why not just follow this with proper risk and money management?

Is this true or am I being totally stupid? Would love to hear from fellow traders and the Zerodha team
@siva-reddy @Bhuvan @nithin @rupeshmandal

Test your strategy with high volatility and low volatility stocks. If it works for both, then you are good to go.
If the strategy works good on low volatility stocks, then execute only on the filtered low volatility stocks.
High volatility stocks have operators and control the movement.