Los Angeles won the rebounding war 42-31. But that doesn't tell the whole story.
At one point, I believe during the first half, LA had that margin at 31-17. I don't think the Celtics need to be explained the importance of rebounding. Rebounds can stop second chance points from your opponents, or give your own team second chance points.
To have gotten beaten like that on that end of the court should be embarrassing to the Celtics. It's not like they are extremely undersized. Kendrick Perkins is 6'11'', so too is Garnett and Wallace, again, what gives?
This looked to be more of a thing of effort more than anything else. The Celtics seemed to not be motivated to go and fish out the rebounds. They seemed to forget that a defensive stand isn't over until the rebound is secured.
The Lakers scored 16 second chance points, while the Celtics were 0-7 on second chance opportunities. Again, this can't happen if the Celtics want to win. Even if they don't convert their second chance opportunities, if they secure the offensive rebound, it gives LA less shots/possessions, and it gives them less rebounds to go and work into their offensive scheme.
The Celtics need to put energy and effort into their rebounding if they want to win.