想象一下：在NBA總決賽上，克里夫蘭騎士隊的勒布朗·詹姆斯剛剛進了一個跳投。然后他又進了一個。又一個。

三投三中，他手感真棒，接下來這球也跑不了，對吧？

大多數人都會毫不猶豫地回答：“對”。但人們的判斷其實和小皇帝的技術沒什么關系，更多來自大腦的猜測。看似一個簡單的預期，其實是長期進化的結果。不過這種預感最大的問題就是準確度不高。從統計數據看，勒布朗投進的可能性并不比打到籃筐彈出去的可能性大多少，跟之前是否連續進球沒什么關系。

這種不假思索就得出結論的現象叫做“近因效應”，深藏在我們的情感脈絡中。杜克大學行為經濟學教授、《可預測的非理性》（Predictably Irrational）等書作者（也是最早提出上述投籃類比的人）丹·艾瑞里說：“這種效應很有趣。人們總是看最新的證據，過于當真，而且預計后面會發生同樣的事。”

“近因效應”在進化上有優勢。回想人類祖先在非洲大草原上的生活：如果某個水源點連續幾天都有角馬出沒，很有可能人們會繼續去那打獵。如今我們坐在計算機前不用再外出打獵，卻仍然本能地在最近發生的事件中尋找規律，較久遠的記憶對我們行為的影響則較小。

當然了，問題在于角馬并不會總在同一地點出現。所以近因效應對投資者來說很特別危險，一個不留神就會變成為人們大腦中錯估投資方向的罪魁禍首。理智上，我們都知道本世紀已經出現了兩次大熊市，分別是在2000-2002年和2007-2009年。然而今年3月，現代史上持續時間第二長的牛市即將進入第八個年頭，近因效應可能會給我們一種虛假的安全感，特別是看到過去三、四年非常高的回報以后。艾瑞里指出：“想想資產泡沫形成的過程就會發現，情況往往如此。市場上漲再上漲，我們就開始認為會一直漲下去。”

市場專業人士也難免受這種思維方式影響。2008年初，全球經濟乍現疲軟之勢。但在連續五年實現正回報以后，股票分析師的信心也升至歷史高點。研究機構Bespoke Investment Group最近的研究顯示，當時華爾街一致認為市場還能上漲11.1%。大家應該想到了，分析師的預測主要依據也是近期行情。我們也都知道接下來發生了什么——經濟斷崖式下跌，當年標普500指數跌去了38.5%。

近因效應還有助于解釋貪婪或恐慌行情中散戶的行為。投資研究公司TrimTabs Investment Research首席執行官大衛?桑茨奇指出，資產流入經常出現在股市就要見頂時，流出則經常出現在市場底部，正好跟投資者應該采取的操作相反。最近的情況就讓人感覺不妙——基金研究機構晨星的數據顯示，去年12月流入美國股票共同基金的資金達278億美元，是2000年4月科技股臨近崩盤以來月度流入最高記錄。

行為經濟學家、加州大學洛杉磯分校教授什洛莫·本納茨認為，快要退休的投資者特別容易受近因效應的影響，然而臨近退休正是最虧不起大把錢的時候。這是衰老應對機制的一部分——如果一生中總是接連不順，感到無能為力，人們就會失去生活的勇氣。但往往牛市接近尾聲時投資者的決策最容易過度樂觀，承擔巨大的風險。

對于未來，估計專家也算不準熊市什么時候來——話說回來，確認沒人說對過。那么，我們怎樣才能抵御并削弱近因效應的影響，不讓過于樂觀（同樣的，過于悲觀）的傾向對決策產生不利影響呢？初學者可以讓證券投資進入“自動駕駛”模式，剔除情緒波動因素。目標日期基金或許是個選擇，這種基金會自動調整投資配置，隨著持有人年齡的增長降低投資風險。Betterment和Wealthfront等智能投顧機構也能幫上，只要提前設置好就能在某類資產的價格達到不正常水平時自動讓證券投資重新回歸平衡。多倫多大學行為經濟學家麗莎·克雷默說：“我熱愛所有阻止人們沖動決定的投資方法。”

歷史數據也是決策時值得考慮的因素。摩根大通資產管理指出，牛市平均長度為54個月，比截至今年1月的奧巴馬-特朗普行情短41個月。標普500指數的長期平均市盈率呢？只有15倍，而目前的市盈率已經超過25倍。這些長期指標表明，要維持目前的估值和市場的良好表現并不容易。

正因為如此，如果市場下跌，一定要確保所有操作都是根據長期計劃，而不是CNBC最新報道傳播的情緒。主要指數不斷破記錄的時候就是投資者進行調整的良機。如果總投資中股票的比重已經從60%的目標值一路上升，已經達到比方說75%，可以賣掉一部分股票鎖定利潤，把資金投入市場滑坡時較為堅挺的資產，比如投資級債券。年紀大一些的投資者可以把資金轉移到風險更小的資產中，比如現金或年金。

Fuller & Thaler Asset Management研究主管拉斐·吉歐凡納佐認為：“投資時千萬不能跟著情緒走，就像希臘神話中駕船穿過塞壬海妖歌聲的奧德修斯一樣。用蠟堵住耳朵，把自己綁在桅桿上，否則只能眼睜睜跟著市場一瀉千里。”

怎樣克服既有思維定勢

包括“近因效應”在內，根深蒂固的思維習慣可能影響投資者的決策，導致投資蒙受損失。以下三種方法可以盡量克服。

價格高時要當心

如果價格/市盈率高得離譜，經常意味著股票上漲時間有些過長。目前股票價格已經遠高于平均水平，或許是個賣出大漲股落袋為安的好機會。

為了退休安全操作

退休前后幾年是投資損失對長期計劃影響最嚴重的時候。處在這個階段的人應該考慮把資金更多地配置在現金和債券上，不管感覺市場有多牛。

依靠“自動駕駛”

在興奮狀態下，阻止沖動型買賣的工具會很有用。目標日期基金、“智能投顧”以及年金都可以幫助投資者避免在牛市中冒太多風險，或者在熊市中恐慌拋售。

作者：Chris Taylor

譯者：Charlie

審校：夏林

Picture this: It’s the NBA Finals, and LeBron James has just drained a jump shot for the Cleveland Cavaliers. Then he hits another. And another.

He’s on a hot streak: three in a row. He’s going to hit the next one, right?

Most people would unhesitatingly reply, “Yes.” That assumption doesn’t say as much about King James’s skills as it does about the inner workings of your own brain. Indeed, a whole lot of evolutionary history is packed into that projection. But here’s the thing about that hunch: It’s off the mark. Statistically, LeBron isn’t significantly more likely to make the shot than he is to clang it off the back rim—streak or no streak.

This leaping-to-conclusions phenomenon is called “recency bias,” and it’s deep in our emotional wiring. “It’s an interesting effect,” says Dan Ariely, a professor of behavioral economics at Duke University and the author of books including Predictably Irrational (and the originator of the hoops analogy). “We look at the most recent evidence, take it too seriously, and expect that things will continue in that way.”

There’s an evolutionary advantage to this. Think back to the origins of humanity somewhere on the African savannas: If the wildebeests have shown up at the same watering hole a few days in a row, odds are we’re going to hunt at that same spot the next day. Nowadays, though we’re hunched at computers instead of hunting game, we still instinctively seek patterns in the events that have happened most recently, while memories of older occurrences have less influence over our behavior.

The problem, of course, is that the wildebeests don’t always come back. And that makes recency bias particularly dangerous for investors: Unchecked, it’s your brain’s very own portfolio killer. Intellectually, we know that the market already saw two brutal bear markets this century—in 2000–02 and 2007–09. But as we approach the eighth birthday in March of the second-?longest bull market in modern times, recency bias can lull us into a false sense of security, especially given the very good returns of the past three or four years. “If you think about the creation of asset bubbles, that’s always what happens,” Ariely says. “Things go up and up and up, and we start thinking it has to always go up.”

Market professionals are hardly immune to this trend. At the beginning of 2008, trouble signs were emerging in the global economy. But after five straight years of positive returns, sentiment among equity analysts neared an all-time high, with the Wall Street consensus calling for an 11.1% gain, according to a recent study by Bespoke Investment Group. Their calls were based in part on—you guessed it—analysis of the recent past. We all know what happened next: The economy went off a cliff, and the S&P 500 fell 38.5% that year.

Recency bias also helps explain retail investor behavior during times of greed or panic. Assets often flow into stocks near market tops and exit at the bottom—exactly the opposite of what investors should be doing, says David Santschi, CEO of TrimTabs Investment Research. Recent signs here aren’t encouraging: Net inflows for U.S. stock mutual funds hit $27.8 billion in December, according to fund research shop Morningstar—the highest monthly total since April 2000, at the dawn of the tech-stock crash.

Investors can be particularly susceptible to recency bias as they get closer to retirement—?exactly the time when they can least afford big losses. That’s part of the mechanism of coping with aging, according to Shlomo Benartzi, a behavioral economist and UCLA professor. If we felt constantly hamstrung by the bad things that have happened to us over the course of our lives, none of us would get out of bed. But those rose-tinted glasses can cloud investing decisions, leading savers to assume too much risk at the tail end of a bull market.

Looking ahead, few experts are predicting the imminent arrival of a bear market—then again, few ever do. So how can you combat and counteract your own recency bias and resist letting excessive optimism (or pessimism, for that matter) hurt your decision-making? For starters, you could put your portfolio on autopilot, taking your mood swings out of the equation. That might mean vehicles like target-date funds, which shift investment allocations automatically to make them less risky as the account holder ages. Also helpful: robo-advisers such as Betterment and Wealthfront, which can be set up to rebalance your portfolio automatically when the prices of one asset class get out of whack. “I’m a big fan of any investing approach that removes us from impulse-based decisions,” says Lisa Kramer, a behavioral economist at the University of Toronto.

It’s also worth keeping historical data in your decision-making arsenal. The average bull-market length is 54 months, according to J.P. Morgan Asset Management—41 months shorter than the Obama-Trump bull run, through January. And the S&P 500 long-term average price/earnings ratio? It’s just 15, compared with more than 25 today. That kind of wider context signals that today’s valuations and recent good times won’t be easy to sustain.

All the more reason to make sure that, if and when the market does turn, any moves you make will be driven by a long-term plan rather than the emotions generated by the last thing you heard on CNBC. With major indexes setting records, it’s a good time for investors to rebalance: If the equities portion of your portfolio has ballooned from your 60% target to 75%, say, take some profits off the table and use them to buy asset classes that are hardier during downturns, like investment-grade bonds. Older investors may want to move that money into assets that are even less risky, like cash or annuities.

“In investing you have to deny your emotions, like Odysseus sailing by the sirens in Greek mythology,” says Raife Giovin?azzo, research director at Fuller & Thaler Asset Management. “Put wax in your ears or tie yourself to the mast—otherwise, you’re going to drown along the cliffs.”

How to Beat Your Biases

Deep-rooted mental habits, including “recency bias,” can throw off investors’ decision-making and hurt their portfolios. Here are three ways to keep those habits in check.

Watch out for high prices

Unusually high price/earnings valuations are often a sign that the party for stocks has gone on a little too long. With stocks trading well above their averages, now may be a good time to sell big winners and put the profits aside.

Play it safe for retirement

The years immediately before and after retirement are when losses can hurt an investor’s long-term plans the most. Savers in that life stage should consider putting more money in cash and bonds—no matter how bullish they feel.

Rely on an autopilot

When emotions run high, it helps to have tools that discourage buying or selling on impulse. Target-date funds, “robo-advisers,” and annuities can help investors avoid taking excessive risks in good times or panic selling in bad.