Martingale: What It Means

A martingale system multiplies its position, often by two, each time a trade loses. One winning trade then recovers all earlier losses plus a small profit. This produces a smooth-looking record with many small wins.

The weakness is that the position size grows very fast. A run of losses, which will happen eventually, can require a position larger than the account can support. The account is then wiped out in a single streak.