Bill Russell has some wise insights into the importance of defense and how it affects a team's psychology. He's too polite to say this, though: on his teams, when the defense was superb, there were always guys around who were also highly skilled offensive players: Bob Cousy, Bill Sharman, Tom Heinsohn, Sam Jones, John Havlicek, and Don Nelson, to name a few. And you could add Russell to that list, because when scoring was critical, he could do it, too.
There is no doubt that the Celtics won largely because of defense. But unlike most NBA teams today, they were fully prepared to exploit the opportunities their defense presented. And they knew what to do - and not to do - in game-winning situations.
When you watch a game today, you see it riddled with errors, and errors at key junctures, too. It's sad, and must drive guys like Russell crazy.