Sometimes it’s the smallest of things — say, about the size of a rut in the Garden ice — that can shift an entire playoff series, an entire season, an entire team’s destiny. So maybe, just maybe, that supposed rut in the ice on Thursday night that forced Bruins goalie Tuukka Rask to fall over on his butt and allowed Carl Hagelin’s deflected dribbler to cross the goal line gave the Rangers just enough of a charge to shift the momentum, not just of that Game 4, but of the whole of this Eastern Conference semifinal. At the very least, it gave the Rangers a heartbeat to come back in that game and win 4-3 in overtime, forcing the next step in this do-or-die sequence, Game 5 tonight in Boston with the Bruins still holding a 3-1 lead that suddenly seems less commanding in this best-of-seven contest. “Bottom line is, all is forgiven, you don’t go back and dissect it,” coach John Tortorella said after yesterday’s practice in Westchester. “We talked about it before the game. We just wanted to get to Boston. We did. Now we need to try to win a game in Boston, and we’ll see where we go from there.” For sure, that Hagelin goal — or more appropriately, that Rask gaffe — is all but distant memory unless the Rangers can back it up. Over the past two postseasons, they’re 6-1 in elimination games, including taking Games 6 and 7 of the first round this year against the Capitals. “I guess in the back of your head you know there’s no turning back, there’s no option,” said Henrik Lundqvist, who managed to creep his postseason overtime record to 4-11. “You have to leave everything out there.” It’s a strange phenomenon, these elimination games. Some say it speaks to the mettle of a team that fights them off, as the Rangers have done so dutifully. “I think we find a way. We’re resilient. We’re not a team that’s going to quit,” said Brian Boyle, who scored the game-tying goal on a third-period power play. “But I don’t really know the exact answer.” There wasn’t a direct answer from the team in light of Brad Richard’s healthy scratch, either, as the alternate captain and former Conn Smythe winner was benched in Game 4 in favor of some fourth-line grinders. If Tortorella’s goal with that move was to light a fire underneath his team, it didn’t work.