“低買高賣”是一個著名的利用市場傾斜在上升和下降過程中賺取利潤的格言。盡管它非常簡單，但是卻很難操作。在回顧時很容易看出特定點的高低，但是在當時，確是非常困難的。價格影響市場參與者的心理和情緒。
因為這個原因，“低買高賣”的持續執行是具有挑戰性的。交易員可以使用工具，例如移動平均數和商業週期。
低買高賣中存在的困難
有著名的市場被驅動到極端的例子，市場泡沫中的高價和市場恐慌中的低價。這些被證明是低買高賣很好的機會。然而，已經發生了無數次市場持續在一個方向上的趨勢，懲罰那些尋求低買高賣機會的人。在一天看起來是高點的價格在另一天看起來可能是低點。
交易員和投資者必須有一個特定客觀方式判斷價格是高還是低。人們習慣於隨波逐流。持續低買高賣有固有的困難。當價格低時，對股票的情緒往往都是相當負面的。許多看漲持有人被迫抛售他們的股票。相同的，當價格低時，很難想象讓一個贏家放手。
低買高賣在某種方式上被誤導，因為低價和高價只用在回顧時才變得明顯。總有看漲的人認為股票價格很低，看跌的人認為價格很高。通常，雙方都提出令人信服的理由。對交易員和投資者的挑戰是判斷哪只股票由基本面驅動到了極端和哪只股票由情緒驅動。當價格由情緒驅動時均值回歸策略更容易生效。
移動平均數
執行低買高賣策略的一個簡單方式是使用移動平均數。移動平均數完全由價格得到的，而且他們在幫助交易員和投資者判斷股票趨勢時很有幫助。
使用一個較短時間的移動平均數和一個較長時間的移動平均數能夠對交易員低買高賣有所幫助並能保護下行風險。例如，一個普遍的方式是使用50天和200天移動平均數。當50天移動平均數穿過200天移動平均數，則產生一個買入信號。當它穿過相反信號，則產生一個賣出信號。
這對交易員判斷趨勢即將結束時的入場點是十分有效的。低買高賣策略的一個問題是在趨勢完全耗盡之前買入或者賣出。該方法避開了這個問題。
商業週期和情緒
一個低買高賣的方法，更適合使用商業週期和情緒調查作為市場時機工具的長期投資者。市場從恐慌到貪婪的長時間内遵循一個相對一致的模式。恐慌最大時是最好的買入時機，而貪婪則是最佳的高賣時機。
這些極端情況每十年都發生幾次並有驚人的相似之處。這些情緒週期跟隨商業週期。當經濟衰退時，恐懼主導市場經濟活動減少。這是低買的時機。
當經濟週期在膨脹階段，經濟活動增加。通常，人們對未來樂觀。這是高賣的時機。例如消費者信心調查的情緒調查為商業週期提供進一步的預見。
A Look At the Buy Low, Sell High Strategy
By Investopedia | August 14, 2015
"Buy low, sell high" is famous investing adage about taking advantage of the market's propensity to overshoot on the downside and upside. Although it is very simple, it is difficult to execute. It is easy to say whether a certain price is low or high in retrospect, but in the moment, it is monumentally difficult. Prices affect the psychology and emotions of market participants.
For this reason, "buy low, sell high" can be challenging to implement consistently. Traders can use tools, such as moving averages and the business cycle.
Difficulties in Buy Low, Sell High
There are famous examples of the market being driven to extremes, whether it is high prices during market bubbles or low prices during market panics. These proved to be excellent opportunities to buy low and sell high. However, there have been countless times when the market keeps trending in one direction, punishing those looking to buy low or sell high. What look like high prices one day may look like low prices another day.
Traders and investors must have a certain objective method to determine if prices are high or low. Humans are conditioned to follow the crowd. There is inherent difficulty in consistently buying low and selling high. When prices are low, sentiment tends to be overwhelmingly negative towards a stock. Many bullish holders are forced to dump their shares. Similarly, when price is high, it is difficult to conceive of letting go of a winner.
"Buy low, sell high" is misleading in some ways, as lows and highs only become clear in retrospect. There is always a bull who considers a stock price to be low and a bear who considers it high. Often, both sides make compelling arguments. The challenge for investors and traders is to determine which stocks are being driven to extremes by fundamentals and which are being driven by emotions. Mean-reversion strategies are more likely to work when price moves are driven by emotions.
Moving Averages
One simple way to implement a buy low, sell high strategy is with the use of moving averages. Moving averages are derived solely from price, and they are helpful in helping traders and investors determine a stock's trend.
Using a moving average of a shorter duration and one with a longer duration can assist in helping traders buy low and sell high as well as protect downside risk. For example, one common method is to use the 50-day and 200-day moving averages. When the 50-day moving average crosses the 200-day, it generates a buy signal. When it crosses the other way, it generates a sell signal.
This is effective in helping a trader time his entry to the point when the trend is faltering. One issue for buy low, sell high strategies is buying or selling before the trend has fully exhausted itself. This approach sidesteps the issue.
Business Cycle and Sentiment
An approach to buy high, sell low, more suited for long-term investors is to use the business cycle and sentiment surveys as market timing tools. The market follows a rather consistent pattern of moving from fear to greed over long periods of time. Times of maximum fear are the best time to buy stocks, while greed is the optimal time to sell high.
These extremes take place a couple times every decade and have remarkable similarities. These emotional cycles follow the business cycle. When the economy is in a recession, fear predominates as economic activity decreases. This is the time to buy low.
When the business cycle is in its expansion phase, economic activity is increasing. Typically, people are feeling optimistic about the future. This is the time to sell high. Sentiment surveys such as the Consumer Confidence Survey provide further insight into the business cycle.
本文翻譯由兄弟財經提供
文章來源：http://www.investopedia.com/articles/investing/081415/look-buy-low-sell-high-strategy.asp