"It took a lot of hard work and a lot of soul searching," he said Sunday. "I've never been more excited to be back in Spring Training; I've never been more excited to be back on the field. When you're not playing well, the game's not fun. I wasn't having fun last year -- I was hurt and struggling.
"I rediscovered that fun a little bit this offseason," he said. "I feel I'm in the best physical shape I've been in and the best mental state I've been in in a long time. I'm very confident coming into camp and am excited to be part of this new regime."
Part of the change in attitude occurred because of the clinic that he and Lars Anderson conducted in Berkeley, Calif.
"I want to get back to that; I want to get back to playing for fun and playing for the guys and playing for the team," he said. "So much has been on performing on an individual level that I've forgotten the importance of why I play and the reason I play. I'm back to have fun and enjoy it and to win."
The Cubs have had high expectations for Jackson since selecting him in the first round of the 2009 First-Year Player Draft out of the University of California, Berkeley. He batted .297 in 2011 at Triple-A Iowa, but the next season hit .256 and struck out 158 times in 106 games.
Don't ask him about the strikeouts any more.
"It's something I'm not going to acknowledge moving forward," Jackson said. "I can't put a finger on it. The last couple years have been a search for finding myself at the plate and overcoming the pressures I was putting on myself. The strikeouts were in the corner of my mind -- being told I was striking out too much. Not to put the blame on anyone but myself. I'm confident in the adjustments I've made. That's something I can improve on."
The Cubs gave Jackson an offseason program that included improving his mental approach to the game. He addressed that as well as looking at videos of successful players. He hasn't reverted to his old swing, but it's more natural now.
"The changes I was trying to make last year had all the right intentions and all the right cues for me to become a better player," he said. "However, I was fighting my nature, I was fighting who I was as a natural athlete, and I think that made my time at the plate a struggle.
"Having said that, I'm thankful for last year, and I'm thankful for what happened and overcoming the injuries I had and the challenges I had at the plate and on the field. I feel the best I've felt moving into Spring Training."
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.