Sitting on a shelf in Sonny Gray’s locker in the corner of the Boston Red Sox clubhouse is a small black notebook. It holds many of the secrets of the most successful season of Gray’s 14-year career.When the Red Sox added Gray as their No. 2 in the rotation behind Garrett Crochet, many thought it a tall ask for a starter in the backend of his career.Still, Gray has anchored the staff, which has been without Crochet for most of the season. Gray has a 2.78 ERA over 21 starts and has thrown at least six innings in all but six outings.The 36-year-old has implemented a method over the years that has made him successful. Writing things down — his schedule for the day, his workouts, how to attack hitters, notes on his performances — is the key.The process started in 2019 at the suggestion of Cincinnati Reds pitching coach Derek Johnson, who also coached Gray at Vanderbilt University.“DJ always carried a little book with him, taking notes,” Gray said. “He would always just be like, ‘Need to get you one of these.'”Gray initially used index cards and would throw them out at the end of the day. Then he realized organizing in a notebook would be more beneficial. He estimates he has 20 at his house.“You have a reference that you can go back to when you feel like you may get off-tilt,” Gray said. “What did my days look like when things are good?”