Isthmian Canal Commission Chief Engineer John Walker believed when he took over the U.S. project to build the Panama Canal in 1904 that the theory that mosquitoes transmitted deadly Yellow Fever was "balderdash" and eliminating the mosquitoes was a waste of time, money, and manpower. Walker's belief rejected 50 years of evidence from medical research that the Aedes aegypti mosquito spread Yellow Fever. His charge to "get the canal built" encouraged his narrow "get 'er done" focus and amplified his desire to wave away all but the most apparent obstacles to success. What's important is often subtle and murky. When we are led to not look for what's less apparent, we can be led seriously astray.

Yahoo CEO and former Google executive Marissa Mayer believed that she could turn around Yahoo when many others before her could not. Whether turning around Yahoo was possible cannot be known. But what does seem evident is that mental traps made the task even more difficult for Mayer. Her story shows us just how extraordinarily difficult it is for us to "unlearn" what has made us successful when new circumstances demand a different approach.

Mountain climbing guide Rob Hall believed that his expedition plan would get Mount Everest climbers in his charge onto and down from the summit. Yet, many climbers found themselves descending in darkness, well past midnight, as a ferocious blizzard enveloped the mountain. Five people died in this highly publicized 1996 disaster and many others barely escaped with their lives. Hall's party encountered the worst of outcomes because options were not recognized and the judgment of others besides Hall went unheard.

PricewaterhouseCoopers' partner and accountant Brian Cullinan believed that he and his associate were well prepared to properly dole out the envelopes with winners' names to presenters at the 2017 Oscars ceremony. Cullinan made the biggest Oscar award mistake ever by handing presenter Warren Beatty the wrong envelope. Beatty's on-stage partner, Faye Dunaway, announced “La La Land” was the winner when “Moonlight” was actually the best picture winner. The accounting firm partner was likely entrapped by many mental errors and biases. Working for a big-name firm and having a big title does not protect one from biases and traps. Indeed, it can lead to overlooking evidence and both rash action and stultifying inaction.

Lehman Brothers CEO Richard Fuld believed that the investment bank was adequately capitalized when it increased its leverage from 12-1 to 40-to-1, became a major player in securitizing subprime mortgages, relied on risky credit default swaps for protection and engaged in accounting maneuvers that disguised how much debt the firm had taken on. Also, he believed that the U.S. government would bail out the firm when the policies and actions he had enabled put the firm on the brink of failure in 2008. Contrary to Fuld's belief, Lehman Brothers was woefully undercapitalized as the financial crisis arose. The federal government walked away from an implicit "too big to fail" tag that Fuld and others thought would be applied to the firm. Lehman Brothers failed and Fuld was disgraced. Three big mental traps jump out of Fuld's folly.

Galileo stubbornly believed that Saturn was three planets in close orbit. This belief, which the Italian astronomer clung to until he died, belied what otherwise was his use of the scientific method: Other astronomers with stronger telescopes reported that what he saw as multiple planets was instead one planet with previously unknown rings around it.. Multiple mental traps and errors may have clouded Galileo's vision.

Samsung's leaders believed that the smartphone giant had a winner when it introduced its flagship Galaxy Note 7 smartphone with a new longer life lithium-ion battery.  After weeks of reports of phones bursting into fire, Samsung issued two separate recalls and ultimately had to permanently withdraw the phone from the market. Here are the mental traps and errors that likely misled Samsung's leaders.

Uber Technologies CEO Travis Kalanick believed that through confrontation he could make the firm supreme and dictate the rules for ridesharing and driverless cars. His approach led to a boycott and great reputational damage for the company and for him personally. Kalanick seems to be a "poster child" illustrating the ill effects of biases and traps.

Hillary Clinton's campaign team believed that with Donald Trump as her opponent she would be elected President. Winning the popular vote did not produce the victory that her team predicted: Clinton lost in the Electoral College. Here are some mental traps and fallacies that likely led the Clinton team to err and predict victory.

Confederate General Robert E. Lee believed that his troops could overrun the Federal's front line at the battle of Gettysburg.  He was wrong: Pickett's charge by 15,000 Confederate soldiers against 6,500 entrenched Federals resulted in over 6,000 Confederate casualties and ended Lee’s last invasion of the north.   Here are several traps and errors that may have led Lee to believe the charge would succeed.