There are trading strategies, such as Momentum, Swing trading, Trend Following, and many more. Each of them can be profitable. The size of the profit depends not on the type of the strategy but on the strategy itself.
Martingale is a money management system originally used in gambling. In this system, the betting starts after a certain number of the same event taking place. For example, in a roulette, after a string of black numbers people start betting on the red. The bet size is doubled after each loss in the hope that the streak is about to end.
The problem with this strategy is that the bet size increases too fast and the player runs a big risk of running out of money before the streak ends.