The letters are a unique display of gratitude, Nooyi explains on "The David Rubenstein Show." And they have had quantifiable results.
When Nooyi first became CEO of the now $150 billion company back in 2006, she visited India, where she had grown up, to see her mother.
"When I got home and I sat in the living room, a stream of visitors and random people started to show up," Nooyi tells Rubenstein. "They'd go to my mom and say, 'You did such a good job with your daughter. Compliments to you. She's CEO.' But not a word to me."
Besides a short greeting, the visitors didn't speak to Nooyi at all.
Nooyi realized that it was her mother and her late father who were responsible for much of her success. They deserved to reap the praise.