There is one area of unanimous agreement in the aftermath of Terry Francona's departure as manager of the Red Sox. No matter what one's view of his exit, everyone agrees that when he was hired as the replacement for Grady Little after the 2003 season, Francona was the perfect man at that point in time to help steward the Red Sox to a championship.

And then, over time, he became something more. In 2007, in his fourth year as the Red Sox manager, he solidified his place in managerial history by guiding a separate -- and changed -- team to a title. That made Francona one of 30 managers ever to claim a pair of titles, and helps to explain some of the shock that has greeted both his departure and his own claims that he no longer felt like he could lead the Red Sox.

The reality, however, is that what Francona experienced in his eighth season as a Red Sox manager is not at all shocking in the context even of great managers. The job becomes harder over time.

A manager is hired to respond to a unique set of circumstances. Through the seasons, the circumstances of the job -- the makeup of the team, the demands on time, the makeup of the front office, the goals of the organization, the competitive environment in which in-game strategy takes place -- change. And it's extraordinarily rare that the same manager can remain the right leader for a team over broad stretches of time, with the ability to evolve while handling the pressure of the job and maintaining the necessary energy and engagement to deal with the challenge.

Francona's tenure had reached a point when managers almost never win the ultimate prize. Of the last 50 World Series, only four have been claimed by a manager who was at least eight years into his continuous tenure with a team. The four:

2006 Cardinals - Tony La Russa (11th season)

1988 Dodgers - Tommy Lasorda (12)

1965 Dodgers - Walter Alston (12)

1963 Dodgers - Walter Alston (10)

That's it. Just eight percent of the last 50 championships, dating to 1960, have been won by managers who were as far into their time in one clubhouse as Francona was in Boston in 2011. Meanwhile, 30 of the last 50 World Series (60 percent) have been won by managers in their first three years on the job.

At first glance, one can look at that information in two ways.

The first is to conclude that managers typically suffer from diminishing returns over time, and that the likelihood is that unless they're a Hall of Famer like Alston who won four championships (two in his first seven years, and two more in his final 16), the longer the managerial tenure, the less effective the manager. 

But the second interpretation resists that reaction, and insists that those raw numbers are misleading, since few managers are deemed good enough to last more than seven years with one club.

Compelling arguments can be made for both views. But, digging a bit deeper, it becomes clear that managers, by and large, reach a point in their tenures when they become less likely to win championships than individuals who are relatively new to the job.

One way to make greater sense of the matter is to ask whether an elite manager -- someone who is so good that he keeps his job for eight or more years -- is more likely to win a championship than a newly hired one. So what do the numbers say?

In the last 50 championship seasons (a category that excludes 1994, when the World Series was cancelled due to the strike), there have been 1,284 different teams chasing a title.

Of those, 148 were managed by someone who was in at least his eighth year on the job, resulting in four championships. The other 1,136 teams, which produced 46 championships, were headed by managers who were in their first through seventh season in the dugout.

How does that break down? On average, managers in years 1-7 won the World Series in 4.05 percent of their seasons. The average manager who had been on the job for eight or more seasons claimed titles in just 2.70 percent of their seasons. In other words, the likelihood of a title was 50 percent greater for a manager in his first seven seasons with a club than it was for the elite managers who managed to hold onto their jobs for eight or more years.

Bobby Cox won his only World Series with the Braves in Year Six, then never won another title in his remaining 15 years in Atlanta's dugout. Both of Francona's World Series came in his first four years in Boston. All four of Joe Torre's World Series titles with the Yankees occurred in his first five years managing in the Bronx.

Typically, the managers who last eight or more seasons do so because they won early in their tenure, but without any real evidence that they can sustain that success. Of the 37 managers since 1960 who have spent at least eight straight years in charge of the same team, between years 1-7, those skippers claimed titles in 9.65 percent of their seasons -- an outstanding rate that is more than double their more short-lived peers. But at the eight-year point, the rate of championship returns dropped to roughly one-quarter of the rate that those elite skippers exhibited during the first seven seasons of their tenure.

All of that suggests that, while Francona's departure may have seemed like a bolt from the blue, perhaps it should not have been. The Red Sox manager had reached a point in his Boston career when the challenge of maintaining his hold on a clubhouse, team and run of success is greater.

Francona said several times in his exit press conference that the Sox might simply have needed a new voice in their clubhouse. History suggests that he was right.

Whatever the reason, the odds of a new manager finding success in Boston are greater than those that Francona would have faced had he lasted another year or two in Boston. Managerial change may not have been expected by the Sox, it may nonetheless represent a productive outcome.