Elite basketball players live in a shrunken, somewhat manufactured social circle. Paul Pierce and Kevin Garnett started their friendship as teens. Pierce was a slightly chubby 16-year-old from Inglewood, Calif. Garnett was the longest, leanest, most talented 17-year-old in the country, and he was about to move out of Mauldin, S.C. They were introduced by an AAU coach, with the purpose of playing together in a Las Vegas tournament. Old-time schoolboy plot lines obviously don’t apply here, though Pierce nearly convinced Garnett to join him for a year at Inglewood High School. Friendship started in the summer of 1994, and the basketball phase is now on its final, surgically-repaired legs. The end for both players could come as early as this summer, though more likely the next. Pierce’s desire to play with Garnett again was finally satisfied five Augusts ago, and there’s no going back to what he knew prior to the 2007-08 season. The Celtics captain can’t conceive of basketball without KG. He likes the idea of a double retirement ceremony. “I could see us both going out together,” Pierce said recently. “I just couldn’t see myself playing without him. I just see what it’s like when he’s not out there, and it’s a whole different feel. It doesn’t feel right.” For one thing, it feels like losing. For another, finality has crept into Pierce’s thoughts. Garnett has had them, too. His infamous “ya’ll don’t know what I know” comment on the eve of the All-Star Game was a mystery to rival the Sphinx.