As far as we know, Tim Duncan is not a Buddhist. But he practices many its most treasured principles — emotional equilibrium, selflessness, focusing on the moment at hand. Which is why he refuses to look back while the Spurs, set to compete for their fifth title, are still moving forward. “I don’t compare teams,” Duncan said Thursday when asked how this run ranks with the previous four. “I’ll figure it out if we’re blessed to win the championship. As of right now, we’re…right where we want to be, and we want to get four more wins.” Still, Duncan could not avoid reflection on both past and future when the assembled media horde questioned him about the reshaping of his body in recent years, and the impact it’s had on revitalizing a career that is now down to its final seasons. Thanks largely to his stone-faced demeanor, Duncan isn’t often characterized as being passionate or particularly competitive — something his head coach takes issue with. “Anybody who doesn’t credit him that way,” Gregg Popovich said, “is probably an idiot.” It was precisely those qualities, however, that motivated Duncan — with more than $200 million in career earnings, and a resume that ranks among the gaudiest in NBA history — to fight the effects of age rather than ride off into retirement.