Surviving physically in the world, for both humans and animals, requires the ability to anticipate and minimize risk. A monkey that picks up and plays with a poisonous snake will meet a swift demise. The same goes for a driver who habitually fails to stop for red lights or railroad crossing signals.

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Serious dangers abound in the social realm as well, even if the consequences of ignoring social risks are usually non-fatal. A spouse who imperils a very good marriage by having an affair with a work colleague is behaving foolishly (which I define as ignoring an obvious risk). Conversely, an investor who recognizes the pitfalls in a popular but flawed investment scheme is behaving wisely (which I define as recognition of a less-obvious risk).

Some degree of risk-taking is a requirement for success in most endeavors. For example, achieving a loving romantic relationship will not happen unless one is willing to take the chance that a choice of spouse or partner will be a mistake. Similarly, successful entrepreneurs, whether in business or other spheres, are those who are willing to go ahead with a project where eventual success at the outset is usually not guaranteed.

So just as there is a downside to plunging ahead in the face of obvious risk, there is a downside to being totally risk-averse. Thus, the key to success is not so much embracing or avoiding risk as it is the ability to appraise risk — to be able to accurately recognize and balance the potential risks and rewards in important situations.

Which brings us to Donald Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE.

Trump is a man who has an inveterate need to initiate and close deals, and has had obvious success on some of them. But many of his initiatives have been non-starters (Trump steaks, Trump U.), while some of them have produced mediocre results (golf courses are usually not big money producers) and a few projects have been spectacular failures.

Trump’s Achilles’ heel has been an inability to rationally calculate the amount of realizable income needed to offset the ridiculously high debt loads he typically takes on, or to control his need to plunge ahead even in the face of obvious dangers and warnings.

This was most dramatically illustrated in his Atlantic City casino projects, where he was saved from personal bankruptcy only by timely help from his father, and the willingness of bankers to write off huge loans. He came out ahead in the end by his questionable claim of tax credits for losses incurred by others, but he was forced to give up ownership of ego-gratifying parts of his empire such as the Plaza Hotel and Trump Shuttle.

Trump’s inability to recognize or avoid serious risk imposed great hardships on others — banks as well as contractors and workers who got stiffed — and, but for some unforeseeable luck, he came very close to having his entire business wiped out.

Today, Trump owes much of his substantial income to the branding of his name, driven in part by his celebrity as a reality TV star. He is spared from further risk-oblivious initiatives by the fact that few banks are foolish enough to continue lending him mega-dollars and he has no ownership stake in most of the recent real estate on which his name is prominently displayed.

I will save for future op-eds an analysis of the personality, character and cognitive qualities that make Donald Trump such a serial ignorer of risk. (But for having Hillary Clinton Hillary Diane Rodham ClintonDemocratic groups using Bloomberg money to launch M in Spanish language ads in Florida The Hill's Campaign Report: Presidential polls tighten weeks out from Election Day More than 50 Latino faith leaders endorse Biden MORE as an opponent in the 2016 race, he made enough foolish campaign mistakes with his mouth and Twitter finger to have sunk him against almost any other candidate). It is a source of great concern that our country is now in the hands of someone who seems to lack an ability to weigh the consequences of domestic and foreign policy decisions where great risks abound.

While we would like leaders to accomplish big things, their main job is to avoid doing catastrophically foolish things.

Stephen Greenspan is emeritus professor of educational psychology at the University of Connecticut. His 2009 book “Annals of Gullibility” was the first comprehensive study of the many ways in which people are duped. He lives in Colorado and often serves as a forensic mental health expert in criminal and civil legal proceedings.

The views of Contributors are their own and are not the views of The Hill.