For Pierce, who spent 15 years clothed in Celtics garb, it was especially difficult.
"I loved it here," he said before the game, per ESPN Boston's Jackie MacMullan. "Never wanted to leave."
That feeling Nets fans are getting right now isn't a warm and fuzzy tingling sensation; it's more like a gut-wrenching discomfort in the pit of their stomach.
How else are Brooklyn's faithful supposed to feel? They're constantly reminded they don't hail from Boston, their team's colors aren't black and their coach is a scruffy dude with Casper-ish skin complexion—not a clean-shaven, raspy-sounding decorated veteran like Doc Rivers.
From the moment he arrived, Pierce has been waxing regret. His comments at an introductory press conference in July sounded like an obituary more than they did a desire to start anew, per Bleacher Report's Jared Zwerling:
As CBS Sports' Matt Moore observed at the time, he did not look particularly happy, either:
Pierce's initial reaction was to be expected. The better part of two decades was spent pouring every ounce of energy he had into Boston's future.
Then, suddenly, he was in Brooklyn.
Facing his old team, on his old stomping grounds, couldn't have helped. Pierce hasn't harped on his departure throughout the season, but an overwhelming sense of regret bubbled to the surface in his return.
"You know what?," Pierce quipped, via MacMullan. "I think as long as I'm in the league, it's going to be tough [to come back] because I'm going to have to come back to the Boston Garden. ... When you come back, there's always going to be memories, and there's nothing you're going to do to escape."
Maybe Pierce's next trip to Boston will be easier and less painful. One day, maybe he'll finally move on and embrace life after Boston.
Or maybe that's wishful thinking.
Returning to the city where it all started, where he won his only NBA title, will never be easy. Pierce won't ever be able to fully move on or nonchalantly say hello knowing he never wanted to say goodbye.