Following up on his full-page letter from Sunday's Boston Globe, Theo Epstein, on the day Ben Cherington officially takes over for him, wrote an op-ed piece for that same Globe today. Epstein essentially says that he owes everyone an explanation as to why he is leaving: that this wasn't a reactionary response to the September collapse, that it was something in the making that was hastened along by other elements. Namely, the departure of Terry Francona, and the need of the Cubs for a new GM:
Football legend Bill Walsh used to say that coaches and executives should seek change after 10 years with the same team. The theory is that both the individual and the organization benefit from a change after so much time together. The executive gets rebirth and the energy that comes with a new challenge; the organization gets a fresh perspective, and the chance for true change that comes with new leadership. This idea resonated with me. Although I tried my best to fight it, I couldn't escape the conclusion that both the Red Sox and I would benefit from a change sometime soon.
Epstein didn't quite make it to 10 years as GM -- though he was with the organization for a decade -- and, as mentioned above (and explained in more detail in the piece itself, which as I said, you should read) -- the opening up of the Cubs' GM position (and inevitably the president of baseball ops slot that Epstein now holds) sped up the process by a year, before his contract with the Red Sox ran out.
The second half of the piece is something of an introduction to new GM Ben Cherington, and how Epstein believes that not only is Cherington capable, but he's personally in a better position to be a GM than Theo was when he came to town, as well as... well, not an excuse for September, but reassurance that if Epstein thought anything from that month were to be a long-term issue, he wouldn't be leaving the team now.
On a more personal note, let me just say how much I enjoy a prominent Red Sox figure telling his own story on the way out, and not doing so in response to questions brought up by some other party.