Stop-loss is one of the most easily overlooked but most critical disciplines in trading. Many traders spend a lot of time studying entry timing but lack equal emphasis on exit timing—especially exiting during losses. This is precisely the root cause of most losses. The core purpose of a stop-loss is to control the maximum risk per trade. The market always contains uncertainty. A stop-loss is not an admission of failure but an acknowledgment of the fact that "I don't know what the future holds," and to set an acceptable cost for that. Trading without a stop-loss essentially bets on "this time will definitely be right," and the market's punishment for such bets is often extremely severe. From a mathematical perspective, the difficulty of recovering from a loss grows non-linearly. A 10% loss only requires an 11% gain to recover, a 50% loss needs a 100% gain, and a 90% loss requires a 900% gain. A deep loss without a stop-loss may require dozens of profitable trades to make up for, which can severely distort subsequent trading mindset and decision quality. Stop-loss also plays an underestimated role: protecting mental state. Anxiety, frustration, and revenge trading impulses caused by deep losses are far more destructive than the losses themselves. Many traders are not knocked out by a single large loss but by a series of impulsive actions after a big loss gets out of control. The existence of a stop-loss allows you to remain calm and rational even after experiencing a loss.