Dirk Nowitzki is proof that greatness loves a challenge. Any challenge, as it turns out. “If we were playing for the 12th seed, it probably would be different,” Nowitzki said. “But this way, there’s still something to play for. Obviously, it’s fun to play for something.” Playing for something. It’s what every athlete wants, and what superstars in particular live for. That’s why Nowitzki has been so Dirk-like in the last few weeks. The Mavericks still are on the outside looking in at the playoffs. But they aren’t out of the picture, either. So Nowitzki works and plays his best basketball of the season when the Mavericks need it most. It wasn’t just his 14-of-17 shooting or 35 points against Chicago on Saturday. It’s the eight consecutive games in which he’s shot at least 50 percent. It’s the 20.9 points he’s averaged in the last 14 games, a stretch in which the Mavericks are 10-4. The thought of missing the playoffs clearly is driving him.