Volatility and unpredictability are the most fundamental characteristics of the market. This is the basis for the existence of the market and the reason for the risk in trading. This is an unchangeable characteristic. There is never certainty in trading. All analytical predictions are only a greater possibility. Trading based on this possibility is naturally uncertain. Uncertain behavior must have measures to control the expansion of its risk, and stop loss is thus generated. Successful investors may have different trading methods, but stop loss is a common feature to ensure their success. The world investment master Soros said that capital itself is not risky, only uncontrolled investment is risky. : Know how to stop loss, never fall in love with loss. Stop loss is far more important than profit, because at any time, capital preservation is the first priority and profit is the second. It is effective to establish a reasonable stop loss principle. The core of the prudent stop loss principle is to prevent losses from continuing to expand. Why is stop loss so difficult? It is important to understand the meaning of stop loss, but this is not the final result. In fact, there are many examples of investors setting stop loss but not executing it. In the market, the tragedy of being swept out is almost every day. Why is stop loss so difficult? According to the reflection effect, it is the adventurous spirit of traders that is at work. There are three specific reasons: First, the mentality of luck. Although traders also know that the trend has broken, they are too hesitant and always want to take a look and wait, which causes them to miss the great opportunity to stop loss; Second, frequent price fluctuations will make traders hesitant, and frequent wrong stop losses will leave traders with lingering memories, thereby shaking traders' determination to stop losses next time; Third, executing stop losses is a painful thing, a bloody process, and a challenge and test of human weaknesses. In fact, we cannot be sure whether it is the right state or the wrong state for each transaction. Even if we make a profit, it is difficult for us to decide whether to exit immediately or wait and see, let alone in a loss state. The human instinct of pursuing adventure and greed will make every trader unwilling to make less money, and even more unwilling to lose more. Therefore, strictly implementing the stop-profit and stop-loss plan involves a good trading mentality, that is, the issue of self-discipline.