為什麽需要止損？從Risk/Reward 方麵看看。

https://youtu.be/Sn91B1VJPNc

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經常看到大千的朋友Portfolio 隻有可數的幾個個股，很為他們捏一把汗。

有人會說，你是老幾？　YMYD, 一邊涼快去。

作為一個從業多年的工程師，我們知道設計工程係統比較重要的事情是“Mitigate Failures". 如果你的設計大部分時間工作，有些case 會導致人員傷亡，這樣的產品總有一天會讓公司破產。

同樣的道理可以用於你的Portfolio. 

不說最近的，當年Enron破產時，好些他的員工退休金統統沒了。

扯遠了。

這裏有個文章介紹Risk/Reward計算，可以用於個股投資的評價。

其中關鍵因素是“止損”。通過科學的止損，可以達到減低Risk,　進而讓你的投資Risk/Reward 達到比較統一的，可以接受的水平。這裏必須提到，專業人士不是吃素的。他們要做大量的研究，確認一個投資不會讓公司資金受到巨大損失。

所以，買股票之前，問一下，我的收益可能是多少，可能的損失是多大，值得冒這個險嗎？

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https://www.investopedia.com/terms/r/riskrewardratio.asp

 

Consider this example: A trader purchases 100 shares of XYZ Company at $20 and places a stop-loss order at $15 to ensure that losses will not exceed $500. Also, assume that this trader believes that the price of XYZ will reach $30 in the next few months. In this case, the trader is willing to risk $5 per share to make an expected return of $10 per share after closing the position. Since the trader stands to make double the amount that they have risked, they would be said to have a 1:2 risk/reward ratio on that particular trade. Derivatives contracts such as put contracts, which give their owners the right to sell the underlying asset at a specified price, can be used to similar effect.

 

If an investor prefers to seek a 1:5 risk/reward ratio for a specified investment (five units of expected return for each additional unit of risk), then they can modify the stop-loss order and thus adjust the risk/reward ratio. But it is important to understand that by doing so the investors has changed the probability of success in their trade.

 

In the trading example noted above, suppose an investor set a stop-loss order at $18, instead of $15, and they continued to target a $30 profit-taking exit. By doing so they would certainly reduce the size of the potential loss (assuming no change to the number of shares), but they will have increased the likelihood that the price action will trigger their stop loss order. That's because the stop order is proportionally much closer to the entry than the target price is. So although the investor may stand to make a proportionally larger gain (compared to the potential loss), they have a lower probability of receiving this outcome.

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