"It was tough for me," he said Wednesday before the White Sox took on the Rockies. "It wore on me because I thought I was disappointing everybody -- my teammates, the front office, the coaches and the fans.
"Now, I know what I can do; it's just a matter of going out there and doing it."
That's what Anderson, 25, has been doing since camp opened last month. It's the reason he's drawing rave reviews from Guillen, who had often voiced his frustration with Anderson and his performance.
"The first spring we gave the job to him and he didn't take advantage of it," Guillen said in recounting the past. "I think this year he's making big, big strides. He's making a lot of people open their eyes.
"That's what we expected from him the last three years."
But what they got wasn't a player who could contribute the way the White Sox needed him to. Yet, that past seems far behind Anderson these days, Guillen said. He's seen more maturity and confidence in Anderson than he saw in those up-and-down yesteryears.
Anderson didn't dispute that immaturity might have been an issue. He spent the offseason, he said, trying to focus on the mental side of baseball. He came to Spring Training with a stronger mental approach to everything.
He also came with less pressure on him and a new attitude.
"It's not a careless attitude, but more just go out there and have fun, and do what you would do and not think about stuff you can't control," said Anderson, whom Guillen started in left field on Wednesday. "I think it's helped me so far."
Guillen didn't disagree.
"I think he should be proud of how he's handled himself in Spring Training," he said of Anderson.
Justice B. Hill is a senior writer for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.