The short, easy answer is that they are simply human acting to the laws of Nature which have then been superimposed by man-made morals of hero worshiping, and which the heroes often find difficult to keep.
No man on earth is a god. Every man is just like the next. The only difference between men is their individual elevation by the public into a model that eventually becomes burdensome and difficult to maintain, especially for the more arrogant ones, or the weaker ones - the two extremes of the emotional psyche. But as far as some members of the public are concerned, heroes have accomplished great feats. Ipso facto, they are saintly and immortal! But these men are far from unique with their fall from grace. History is littered with the falling debris of illicit affairs and sex scandals on both sides of the Atlantic.
To begin with, in 2008, Gov. Eliot Spitzer of New York, was virtually caught with his pants down, which kicked off an embarrassing scandal, especially for one so high-powered, well established and respected. Worse still, he had made his name trying to get rid of the very prostitution rings like the one he himself had quietly subscribed to, and was enjoying so salaciously. Impressive and debonair, Spitzer thought he was so powerful, he could afford to ignore his own public standards when it applied to his private life.
In the United Kingdom, back in the early 90s, John Major became the Prime Minister to replace Margaret Thatcher in the Tory party. He turned out to be a fine, caring Prime Minister, on one hand, the butter-wouldn’t-melt type, who was regarded as bland and boring. In fact, the famous satirical TV programme, Spitting Image, always portrayed him as the ‘grey man’, so boring was he perceived by the public. Yet for four years into his leadership, as a married man, and right in the Palace of Westminster, he was having an affair with one of his Junior Ministers, Edwina Curry, under the blandness. He hid it so well, it was not revealed until long after he left office (in the 21st century) - and it was actually Edwina who wrote about it in her Daries, Volume 1: 1987-1992.
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Now we have high ranking David Petraeus and Paula Boadwell. One cannot get higher in public elevation and acclaim than General Petraeus. He had it all: good looks, great accomplishments, great status, great renown and great acclaim. But he obviously lacked something in his life, and it appeared in the form of Boadwell.
So what makes powerful men prone to sex scandals when they are at the top of their tree? When they seem to have everything which other people might envy? What makes them risk their achievements and family life for moments of madness? What prompts them to take such heady risks in the face of all they have to lose? Could it be that it takes a certain kind of very focused individual to get to the top, one who is often self-centred and egocentric; one who believes that their status gives them so much power that the only person who matters is him? That the whole world revolves around them?
Or could it be that the very feat of getting to the top, of besting other men in the process, carries a perception of greater sexual prowess too which also has to be proven and sustained to make that person feel worthy? That they actually 'deserve' everything they get at that level, and it should be theirs for the taking? It seems that power, that elusive attribute most men crave, is an intoxicating aphrodisiac to both men and women. It makes the holders appear even more attractive and desirable, especially power over women and employees.
Life at the top is a different version of life for mere mortals. It carries tremendous pressures of service delivery, public expectations and professional exposure for the incumbents; a need to prove being the best person in that job while the eyes of the public watch keenly for the wrong step that will signal their Achilles heel and, ultimately, their demise. The goldfish bowl of power is a very limiting and exposed place to be - and has loneliness as its hallmark. Power separates and demarcates, and few men can really cope with that isolation and constant expectation of saintliness. Perhaps, men in this situation, charged with so much responsibility need an outlet, or activity, where they can simply forget the world and please themselves. But, paradoxically, the activities tend to be those which appear to carry great risks and also have the power to destroy them, in a perverse kind of death wish!
Whatever it is, these powerful men are a race apart from ordinary mortals in a competitive society. When they get to that level, the trappings of power: willing staff waiting on them constantly, money, perks, high status and the conditions of office, can sometimes go to their heads. A few begin to believe that they are invincible and the rules cease to apply to them. They begin to test the boundaries, to enjoy the thrill of pushing those elastic boundaries hard (the ones they should be stabilising), and then getting away with it, until the day their luck runs out. Then those boundaries have a bad habit of bouncing back to hit them massively in the groin, bringing their world crashing around them with a huge and reverberating bang.