"I don't care if I go 0-for-4, 0-for-5, I want to keep my feeling," Castro said. "That's the only thing I try to do now is don't lose my feeling -- I try to feel good every time."
Cubs manager Rick Renteria was happy to see Castro be proactive.
"A player doesn't want to go out and fail," Renteria said. "They want to perform. They don't like being booed or looked upon that they've failed in a task.
"That's part of his growth and part of him growing up. I would say he's been proactive his whole career. But you have to know how to be proactive and know what to look for. As instructors, we need to know what to ask of the players."
Castro has bounced back from a disappointing 2013 season, batting .270 this season entering Sunday.
"It helps me," Castro said of the extra sessions. "I don't worry about anything. I don't worry about the pitcher. If he gets me, OK. I'll get you tomorrow. I want to stay with that feeling all year."
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.