No rule completely prevents losses in forex, because losses are a natural part of trading. However, one rule consistently minimises damage and keeps traders in the game:

Never risk more than a small, fixed percentage of your account on a single trade, typically 1 percent or less, and always use a hard stop loss.

This rule works because it controls risk before emotions take over. Even profitable strategies experience losing streaks, and without strict risk limits, a few bad trades can wipe out weeks or months of progress. By fixing risk per trade, losses stay manageable, and recovery remains mathematically possible.

In practice, this means calculating position size before entering, placing the stop loss at a logical technical level, and accepting the potential loss upfront. The focus shifts from avoiding losses to managing them properly. Traders who survive long term are not those who avoid losses, but those who control them with discipline and patience.