Although San Antonio came within 5.2 seconds of capturing Duncan's fifth championship in Game 6, the 14-time All-Star said that the Spurs' Game 7 defeat will be the one that sticks with him.
"Game 7, missing a lay-up to tie the game, making a bad decision down the stretch," he said. "Just unable to stop Dwyane [Wade] and LeBron [James]. Probably, for me, Game 7 is always going to haunt me."
With Miami leading 90-88 with just one minute remaining, Duncan missed a hook shot deep in the paint and then was unable to convert point-blank tip-in that would have tied the game.
The Spurs did not score the rest of the way, as James nailed a jumper before the Heat hit three free throws to seal their third title in franchise history. James finished with a game-high 37 points, 12 rebounds and four assists; Wade added 23 points and 10 rebounds.
"The obvious word is 'disappointing'," Duncan said. "Tough end to the game. Made some bad decisions. Missed some shots. I don't know what to say. Just give credit to the Miami Heat. LeBron was unbelievable. Dwyane was great."
Manu Ginobili called San Antonio's Game 6 loss "devastating" after the Spurs gave up a five-point lead in the final 30 seconds before losing in overtime. Duncan indicated after the game that he planned to return for the 2013-14 season rather than retire.