Martingale system is a betting system where you double your bet when you lose. And when you do win, then you would recover all your previous losses and end up with a winning equal to your initial bet. Alot of people like Martingale because it is easy to understand and it gives them a sense of "winning" because the gambler usually end up winning in the beginning before losing everything at the end. This betting systems sound appealing except that in real life it does not work so well due to the following reasons.
There is always a betting limit. The casino and bookmaker will have a maximum limit you can bet on. So... if you run into a string of losses, and you hit the betting limit, then you cannot double the bet anymore.
More often instead of hitting the betting limit, the gamblers lose all their money first in a string of losses. Long streaks of losses is common. A gambler who prepares a capital anticipating a losing streak of maximum 5 hands will be surprised that he is out of funds very fast.
If the Martingale systems really can let you win consistently, then this would mean the casino is losing money consistently. Do you think the casino would let this happen? Of course not. If Martingale really works, then the casino would have banned this betting systems. The fact that the casinos allow this betting systems mean that Martingale does not work. In fact, Martingale more often makes the gambler lose their capital. This means that with a Martingale systems, the casino will win consistently.
If you do happen to win money by using Martingale systems, then it is more so because of your luck, rather than because of the Martingale systems.