You never want a career 25 percent 3-point shooter taking the final shot with the game on the line, open or not. But that’s exactly how the Celtics decided to end Monday night’s game against the Dallas Mavericks, an 89-87 loss. Rajon Rondo had a wide-open look on his attempt, but that was by design. Dallas wants him to take that shot because history suggests that there is a 75 percent chance he’ll miss it. The Celtics and Rondo both should know better.