I think the Celtics over-reliance on flopping to gets calls has finally caught up with them. To me, this is especially true when they drive to the rim. Tatum, in particular, missed a lot of layups all season, but was bailed out by the refs and went to the line. In the Finals, he doesn't seem to be getting those calls. Instead on finessing his way to layups, he should be attacking with force.
Unfortunately, if the Celtics end up losing this series, I think Brad Stevens has to make a major shake-up move. I know this team is in the Finals, but I don't think you can be this close and lose, and recover.