He feels normal again entering the season opener against the Vegas Golden Knights at T-Mobile Arena on Wednesday (10:30 ET; NBCSN, TVAS), setting the highest of standards.
"I think that here the biggest hurdle is, you know, strive for greatness and not just accept being good," Karlsson said. "I think that they've had a lot of good years here in the past, but again, we all play for that one great one."
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The Sharks acquired Karlsson from the Ottawa Senators on Sept. 13, 2018, to help put them over the top. They had been contenders for years but had never won the Stanley Cup. Karlsson was a defenseman who had won the Norris Trophy twice.
But it was a difficult adjustment in hockey and life. The Senators were the only team Karlsson had known in a nine-year NHL career. He was their captain. Ottawa was home. And he was in the last year of his contract.
At midseason, though, he and the Sharks looked like they were expected to look: elite. Then he battled groin injuries.
Karlsson missed 27 of the Sharks' final 33 regular-season games, finishing with 45 points (three goals, 42 assists) in 53 games. He gutted it out for three rounds in the Stanley Cup Playoffs and tied for second on the Sharks with 16 points (two goals, 14 assists) in 19 games.
But in the Western Conference Final, he had to leave Game 5 and sit out Game 6 when the Sharks were eliminated by the St. Louis Blues, who went on to win the Cup.
"Unfortunately [he was] hurt in the playoffs," center Logan Couture said. "Or else I think things could have been different for us."
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At the time, because teams are loathe to discuss injuries in the moment, the Sharks would only hint at how badly Karlsson was ailing. Now coach Peter DeBoer is willing to say Karlsson was probably playing as high as 70 percent of his ability and as low as 40 percent, depending on the night.
"It's hard to play, no matter how great a player you are, when you're dealing with that," DeBoer said.
Karlsson is willing to be more candid too.
"It was brutal," he said. "I found a way to play and still contribute up to a level where I felt that it was helping the team. That's the way it is sometimes. Yeah, it's no fun, but at that time of the year, you do what you have to do. Luckily, got it all sorted out this summer and feel good now."
Karlsson had surgery May 31 and signed an eight-year contract with the Sharks on June 17. It took two or three months before he could do normal activities, and he didn't lift weights as hard as he usually does in the offseason. But he started skating in early August as he typically does.
"So, it's not like it screwed up my preparation in any kind of way, which is good," he said.
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When he arrived in San Jose for training camp, he felt healthy and at home.
"I think last year was a unique year," he said. "It was different. It was something I hadn't gone through before and didn't think I was going to have to go through. But you know, it's in the past now, and I think that I learned a lot from dealing with that experience, and this year probably feels a little bit more normal.
"I've been here for a year. I know most of the guys now pretty well. A lot of things that I had to worry about last year I don't anymore. It's just coming a little bit more automatic. So yeah, that feels good. But again, I think that the learning experience that I had to go through is going to help me become a better man and a better player."
The Sharks look different than they did in the playoffs. Gone is forward Joe Pavelski, who had spent his entire 13-year NHL career in San Jose and was captain. Also gone are forwards Gustav Nyquist and Joonas Donskoi, and defensemen Justin Braun and Joakim Ryan.
"I know we lost a few bodies, which happens to every team, usually," Karlsson said. "We've got to try and evolve a little bit maybe. I think that even the things that we do well can still get better. We've got to keep pushing for that, I think. We have a full year here now to try to build on it and figure it out for when the time comes when you know every game matters a little bit more."
Karlsson will matter a lot.
"He's going to be a huge key for us," DeBoer said. "When he was healthy last year and used to our system and how we want to play, he was as good as there was in the League, and our team was a reflection of that, because he makes other people better.
"So, he's moving effortlessly. He's got no issues with any of the injury stuff that he dealt with over the summer. It's a good sign for us."