In Game 1 of the Eastern Conference finals, the Pittsburgh Penguins were suckered. They did exactly what you shouldn't do against the Bruins, and that's play Bruins hockey.
They scrummed after every whistle, they tossed cheap shots, they tried to be physical and assert themselves that way. You can't beat the Boston Bruins that way.
While you try to out-tough the Bruins, they re-assert that they're stronger than you and beat you with skill. That's how they won the cup in 2011, that's why they're so successful. So many people think the Bruins are great because they're big, but they're great because they're skilled, and they easily draw teams into the sideshow while remaining focused. It would be brilliant if it wasn't so douchey.
The Penguins will have to play their own game to have a hope in this series, and that means turning a blind eye sometimes, answering on the powerplay. Luckily they have guys like Sidney Crosby, Evgeni Malkin, and Kris Letang to help them out there.