Al Horford decided to leave the Celtics regardless of what Kyrie Irving did in free agency last summer. If Irving stayed, Horford deemed Boston's chemistry too problematic. If Irving left (which he did for the Nets), Horford saw the Celtics taking a step back. So, Horford signed with the 76ers.
But Boston rebounded surprisingly well from losing Irving, landing Kemba Walker - another star point guard but one whose personality should fit better. Horford still left for Philadelphia, but he said it would have been "totally different" if he knew the Celtics were getting Walker.
Here's the catch: The cap space Horford vacated was essential in Boston acquiring Walker. The Celtics couldn't have simply gotten both.
But there were ways. Boston reportedly discussed a triple sign-and-trade with the Nets and Hornets involving Walker, Irving and Terry Rozier. That would've allowed the Celtics to acquire Walker while retaining Horford's Bird Rights.
The big question: What was that price? The Nets certainly weren't eager to help a division rival. They could've signed Irving outright (and did). Aiding Boston would've likely required a big sweetener of draft picks.
The Celtics would've been better with Horford. His defense will be sorely missed. But he's also a 33-year-old on an expensive contract. Even if he agreed to return, the cost wouldn't have have necessarily been worth it.
Acquiring a player via sign-and-trade also hard-capped Boston. There was room to fit Horford under that hard cap, but it would've been a tight squeeze. Who knows what other players that arrangement would've cost the Celtics?
Perhaps most importantly, Horford still left even after knowing Walker was headed to Boston. Maybe it would've been different if Horford knew sooner. It's unclear what unofficial commitments Horford made privately. But Walker was a done deal to the Celtics before Horford signed with the 76ers. Horford still could've re-signed if Boston met Brooklyn's demands for a triple sign-and-trade.
He didn't, leaving this as not much more than a fantasy among some Celtics fans.