Sometimes, one season can change the entire statistical arc of an athlete's career without anyone even realizing it; I don't mean when a player goes through a devastating injury or even when he switches teams -- just that his numbers can shift enough to alter our expectations of his future cumulative performance.
I remember after the New York Mets traded Tom Seaver, one of the few pleasures left to me as a young fan was tracking his progress toward 300 wins -- even if he had to pile up his victories for an alien team. After a dozen years in which Seaver was as consistent as a pitcher could be, his win totals started gyrating wildly in his late 30s, and my approximations grew more anxious as he got older.
Having 273 wins and pitching for a lousy team at the age of 39 seemed a lot further away from 300 than having 259 wins for the best team in the league at the age of 37. Of course, the Mets were dumb enough to allow Seaver to get away a second time and he got over the hump with the Chicago White Sox; my point, though, is that even as athletes' career totals increase, they carry with them a second set of expected numbers that can go up or down.
This all brings us to Alex Rodriguez. When I published "Dingers!" my history of the home run, at the start of the 2006 season, I used a method called "The Favorite Toy," which Bill James developed back in the early 1980s, to calculate that A-Rod had an 89 percent chance of hitting 600 home runs and a 30 percent chance, higher than that of anyone else (even Barry Bonds), of breaking Hank Aaron's home run record.