Presidential greatness is not predictable by a candidate's resume or professional background, according to political analysis. While many presidents have served as governors, senators, or generals, there's no correlation between these roles and a president's eventual success. For instance, Ronald Reagan and Jimmy Carter were both governors, but Reagan had a strong grasp of the office while Carter struggled. Similarly, Lyndon Johnson, a former senator, was highly effective in Congress, whereas John F. Kennedy's domestic agenda often stalled. This suggests that the demands of these prior offices, though taxing, do not necessarily cultivate the unique virtues needed for the presidency. Abraham Lincoln, widely considered a great leader, held none of these traditional executive or military positions, further demonstrating this lack of correlation.

The essential quality for a great president is prudence, defined as the ability to perceive opportunities and skillfully leverage them. This involves an intuitive understanding of governmental functions, the interests of other politicians, the nuances of public opinion, and the capacity to guide processes towards desired ends. As Edmund Burke noted, prudence is not a universal abstraction but a practical virtue that allows leaders to make optimal decisions within real-world constraints. Prudence acts as a bridge between the high expectations placed on presidents and their limited formal powers. For example, Franklin Roosevelt's success with the New Deal, especially Social Security, wasn't solely due to his congressional majority but his prudent understanding of how to present it to the American people and build in features ensuring its longevity.

The modern presidency demands significantly more than the Founding Fathers initially envisioned, yet the president's power remains largely informal and extra-constitutional. A president's effectiveness stems from the belief in their power by other government agents. This explains why some presidents, despite having large congressional majorities, like Jimmy Carter, were deemed ineffective, while others, such as Ronald Reagan, achieved much with a divided Congress. Similarly, Bill Clinton was most effective after the "Republican Revolution" of 1994, and George W. Bush struggled to pass significant legislation even when his party controlled both chambers. This adaptability and the ability to influence others, often through prudence, rather than a specific professional history or personality traits like being stubborn or agreeable, truly defines presidential success.

While some research suggests that great presidents may exhibit traits like extraversion, openness to experience, assertiveness, and achievement striving, and are often perceived as stubborn and disagreeable, these are not the sole determinants. Many intellectually accomplished presidents, such as John Adams, Herbert Hoover, and Richard Nixon, performed below expectations or faced significant challenges, including Nixon's forced resignation due to Watergate. Conversely, Lincoln, with a less extensive resume, is revered as one of America's finest. The development of prudence in these successful leaders often remains a mystery; it may stem from prior experience but is not guaranteed by it, highlighting its ineffable nature as the core of presidential greatness.