This effect can be quantified more rigorously. I used data on all 17 current Major League franchises that had been established in their current city by 1965. I modeled the probability of an adult’s supporting a team today based on the adult’s age and gender, the team and how good the team was at every year of his or her childhood. Note that this model takes into account the fact that some teams, like the Yankees and the Red Sox, are more popular at all ages. And it takes into account the fact that baseball fandom, at least as expressed on Facebook, differs by age.

Let’s look at men. The model’s results were striking. They show that the years before a boy’s birth and the first couple of years of his life are, as you would expect, statistically irrelevant to his adult fandom. But then things start to matter in a big way.

The most important year in a boy’s baseball life is indeed age 8. If a team wins a World Series when a boy is 8, it increases the probability that he will support the team as an adult by about 8 percent. Remember, this is independent of how good the team was every other year of this guy’s life. Things start falling off pretty fast after the age of about 14. A championship when a man is 20 is only one-eighth as likely to create an adult fan as a championship when a boy is 8. Just winning games also matters, with a similar age pattern. But the data shows that there seems to be something really special about winning championships.

These results mean a successful team leaves a huge imprint long after all the players are retired. Consider a team like the St. Louis Cardinals. In a five-year period in the 1940s, led by Stan Musial, the Cardinals averaged more than 100 wins a season and won three championships. According to my model, roughly 20 percent of 80-year-old male Cardinals fans today would either support another team or not be a baseball fan if not for Musial and his teammates’ epic run.

Of course, winning is not all that matters for fandom. Long-suffering teams like the Cubs have plenty of fans. But winning helps in a big way, and the Cubs would have far more fans if they had won more.