Al Horford leaving Boston was one of the biggest surprises of the summer. Everyone expected Al to turn down his player option and go into free agency, but it was assumed he would do it to ensure a longer, lucrative contract with the Celtics. To the surprise of many, including the Celtics, Horford signed with the 76ers.
In an interview with Steve Bulpett from the Boston Herald, Horford said the Celtics were his priority, but when they couldn't agree on a number, he realized he would have to open his free agency. He felt the team underachieved, but what held them back was they had too much talent, and the team couldn't find a way to make it work. Still, there was an obvious elephant in the room:
"And we all kind of felt that Kyrie (Irving) was going to leave. It was like, maybe he’ll stay, but then it was, nah, he’s probably going to leave just based on how everything was."
It was exhausting covering Kyrie and all his mood swings, so it must've been even worse being in the locker room going through all that. As the veteran on the team, Horford was expected to stabilize everything, and that wasn't an easy thing to do. There was a chance Kyrie might decide to stay, but that wouldn't change Horford's decision:
“I’m not sure that has anything to do with it for me,” Horford said. “I just think that if Kyrie would have stayed, I don’t know if it would have worked. There would have had to be some major changes as far as players, because it was just clear that the group that we had just wasn’t going to be able to coexist.”
If you doubted it before, here's another proof that chemistry is a thing and has to be a consideration when building a team.