Illustration: How to develop a sustainable trading strategy
The secret dream of any trader is surely to develop a long-term winning strategy that works on any market. Such a strategy is called a martingale.
It is possibly good to examine exactly what a Martingale Strategy is here.
It was initially a betting style popularised in 18th century France as, to many gamblers, it ‘appeared’ to be quite literally a sure bet 
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In the 1930’s a French mathematician, Paul Pierre Levy, worked on a probability theory based on this betting style, in part to prove that such a strategy was in fact doomed to fail and inevitably bankrupt the gambler. The theory was further developed and proven by Jean Ville and an American, Joseph Doob. (Here endeth the history lesson 
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Probably the biggest single disadvantage of Martingale strategies is that they are based on cost-averaging - they don’t rely on any predictive ability input from the trader. In simple terms the trader doubles the trade size after every loss until a single winning trade occurs. At that point, because of the mathematical power of doubling, the trader hopes to exit the position with a profit.
The principle problem with such a strategy is that what might appear a substantive trade then drains your account before you can turn a profit or even recoup your losses. At this point, any sensible trader must question whether they are willing to lose most of their account equity on a single trade. Given that they must do this to average much smaller profits, many feel that the martingale trading strategy offers more risk than reward. To me, as a standalone strategy, it will always remain an extremely high-risk one that I avoid at all costs.
Any gains are based purely on mathematical probability over time instead of relying on any acquired underlying knowledge and experience in particular markets - these latter factors being those which (in my opinion) differentiate the successful trader from the novice trader.
So, as attractive as it may sound, a great deal of caution is needed for those who consider practicing the Martingale strategy 
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This is why it should always remain, as Carlo has correctly insinuated, a secret dream strategy.