(John Paul Filo / AP photo / CBS)

When certain other big-name big men are opting out, Tim Duncan is opting in.

Duncan plans to return for his 18th NBA season with the San Antonio Spurs and, after they demolished the Miami Heat in winning the NBA title, why on earth wouldn’t he? By anyone else’s standards, reaching the age of 38 with five championships might be a good time to call it a career. But Duncan plays for a team that epitomizes “team” and for a coach who knows how to get rest for an aging core of stars during the regular season (even if it gets him fined). Why go out on top when there’s a chance to out after a repeat — or a threepeat?

Duncan explained this and a few other things to David Letterman in a “Late Show” appearance Monday night, admitting that he thought about retiring but decided to exercise his option for another season because he felt he “could at least do one more year. I felt I was still effective. I felt I could still help the team.”

Duncan’s player option is worth $10.3 million, probably half what LeBron James will make with some team. Back in San Antonio on Monday, this billboard sprang up after James’ decision to opt out of his contract.