“Stay level-headed,” Grant Williams said when asked how the Celtics have managed to survive the peaks and valleys of the playoffs so far. “At the end of the day, no matter what happens, whether it’s a big win or big loss, you have to play it the right way. We can’t let it carry over. It’s 2-1 right now and we play in front of our Garden fans and can make it 2-2. “It’s one of those things where we still control our destiny. We have to come out there and not only be a little more physically dominant and be more conscious of what we are trying to accomplish. Just like a regular season, there’s going to be peaks and valleys, you are going to have success and times you are not playing well, but the best teams stick together through thick and thin and they do their best job understanding the same thing can’t beat you twice.”